diff --git a/ApplicationCode/ProjectDataModel/Summary/RimDerivedEnsembleCaseCollection.cpp b/ApplicationCode/ProjectDataModel/Summary/RimDerivedEnsembleCaseCollection.cpp
index 7c1622bf4b..805bd86ac4 100644
--- a/ApplicationCode/ProjectDataModel/Summary/RimDerivedEnsembleCaseCollection.cpp
+++ b/ApplicationCode/ProjectDataModel/Summary/RimDerivedEnsembleCaseCollection.cpp
@@ -120,13 +120,13 @@ std::vector<RimSummaryCase*> RimDerivedEnsembleCaseCollection::allSummaryCases()
 //--------------------------------------------------------------------------------------------------
 /// 
 //--------------------------------------------------------------------------------------------------
-std::set<RifEclipseSummaryAddress> RimDerivedEnsembleCaseCollection::calculateUnionOfSummaryAddresses() const
+std::set<RifEclipseSummaryAddress> RimDerivedEnsembleCaseCollection::ensembleSummaryAddresses() const
 {
     std::set<RifEclipseSummaryAddress> addresses;
     if (!m_ensemble1 || !m_ensemble2) return addresses;
 
-    addresses = m_ensemble1->calculateUnionOfSummaryAddresses();
-    auto addrs2 = m_ensemble2->calculateUnionOfSummaryAddresses();
+    addresses = m_ensemble1->ensembleSummaryAddresses();
+    auto addrs2 = m_ensemble2->ensembleSummaryAddresses();
     addresses.insert(addrs2.begin(), addrs2.end());
     return addresses;
 }
diff --git a/ApplicationCode/ProjectDataModel/Summary/RimDerivedEnsembleCaseCollection.h b/ApplicationCode/ProjectDataModel/Summary/RimDerivedEnsembleCaseCollection.h
index 6681dd0fda..edf77e0834 100644
--- a/ApplicationCode/ProjectDataModel/Summary/RimDerivedEnsembleCaseCollection.h
+++ b/ApplicationCode/ProjectDataModel/Summary/RimDerivedEnsembleCaseCollection.h
@@ -53,7 +53,7 @@ public:
     void                        setEnsemble2(RimSummaryCaseCollection* ensemble);
 
     virtual std::vector<RimSummaryCase*>    allSummaryCases() const override;
-    virtual std::set<RifEclipseSummaryAddress> calculateUnionOfSummaryAddresses() const override;
+    virtual std::set<RifEclipseSummaryAddress> ensembleSummaryAddresses() const override;
     void                                    updateDerivedEnsembleCases();
     bool                                    hasCaseReference(const RimSummaryCase* sumCase) const;
 
diff --git a/ApplicationCode/ProjectDataModel/Summary/RimSummaryCaseCollection.cpp b/ApplicationCode/ProjectDataModel/Summary/RimSummaryCaseCollection.cpp
index c5776a9778..7206c3af90 100644
--- a/ApplicationCode/ProjectDataModel/Summary/RimSummaryCaseCollection.cpp
+++ b/ApplicationCode/ProjectDataModel/Summary/RimSummaryCaseCollection.cpp
@@ -170,26 +170,34 @@ void RimSummaryCaseCollection::setAsEnsemble(bool isEnsemble)
 //--------------------------------------------------------------------------------------------------
 /// 
 //--------------------------------------------------------------------------------------------------
-std::set<RifEclipseSummaryAddress> RimSummaryCaseCollection::calculateUnionOfSummaryAddresses() const
+std::set<RifEclipseSummaryAddress> RimSummaryCaseCollection::ensembleSummaryAddresses() const
 {
-   std::set<RifEclipseSummaryAddress> addressUnion;
+   std::set<RifEclipseSummaryAddress> addresses;
+   size_t maxAddrCount = 0;
+   int maxAddrIndex = -1;
 
-   for (RimSummaryCase* currCase: m_cases)
+   for (int i = 0; i < (int)m_cases.size(); i++)
    {
-       if ( !currCase ) continue;
-       
+       RimSummaryCase* currCase = m_cases[i];
+       if (!currCase) continue;
+
        RifSummaryReaderInterface* reader = currCase->summaryReader();
+       if (!reader) continue;
 
-       if ( !reader ) continue;
+       size_t addrCount = reader->allResultAddresses().size();
+       if (addrCount > maxAddrCount)
+       {
+           maxAddrCount = addrCount;
+           maxAddrIndex = (int)i;
+       }
+   }
 
-       const std::set<RifEclipseSummaryAddress>& readerAddresses = reader->allResultAddresses();
-       addressUnion.insert(readerAddresses.begin(), readerAddresses.end());
-
-       // We assume that all cases have the same addresses when they have equal number of addresses.
-       // In that case there is no need to calculate the union, we only use the addresses from the first case
-       if (m_commonAddressCount > 0) break;
-    }
-    return addressUnion;
+   if (maxAddrIndex >= 0)
+   {
+       const std::set<RifEclipseSummaryAddress>& addrs = m_cases[maxAddrIndex]->summaryReader()->allResultAddresses();
+       addresses.insert(addrs.begin(), addrs.end());
+   }
+   return addresses;
 }
 
 //--------------------------------------------------------------------------------------------------
diff --git a/ApplicationCode/ProjectDataModel/Summary/RimSummaryCaseCollection.h b/ApplicationCode/ProjectDataModel/Summary/RimSummaryCaseCollection.h
index 3fa0e59d6c..fb6939b538 100644
--- a/ApplicationCode/ProjectDataModel/Summary/RimSummaryCaseCollection.h
+++ b/ApplicationCode/ProjectDataModel/Summary/RimSummaryCaseCollection.h
@@ -72,7 +72,7 @@ public:
     QString                         name() const;
     bool                            isEnsemble() const;
     void                            setAsEnsemble(bool isEnsemble);
-    virtual std::set<RifEclipseSummaryAddress> calculateUnionOfSummaryAddresses() const;
+    virtual std::set<RifEclipseSummaryAddress> ensembleSummaryAddresses() const;
     EnsembleParameter               ensembleParameter(const QString& paramName) const;
     void                            calculateEnsembleParametersIntersectionHash();
     void                            clearEnsembleParametersHashes();
diff --git a/ApplicationCode/UserInterface/RiuSummaryCurveDefSelection.cpp b/ApplicationCode/UserInterface/RiuSummaryCurveDefSelection.cpp
index a3407e15fd..2755cd47ed 100644
--- a/ApplicationCode/UserInterface/RiuSummaryCurveDefSelection.cpp
+++ b/ApplicationCode/UserInterface/RiuSummaryCurveDefSelection.cpp
@@ -273,7 +273,7 @@ std::vector<RiaSummaryCurveDefinition> RiuSummaryCurveDefSelection::allCurveDefi
             // Build case list
             if (ensemble)
             {
-                auto addresses = ensemble->calculateUnionOfSummaryAddresses();
+                auto addresses = ensemble->ensembleSummaryAddresses();
                 addressesFromSource.insert(addresses.begin(), addresses.end());
                 auto ensembleCases = ensemble->allSummaryCases();
                 casesFromSource.insert(casesFromSource.end(), ensembleCases.begin(), ensembleCases.end());
@@ -324,7 +324,7 @@ std::vector<RiaCurveSetDefinition> RiuSummaryCurveDefSelection::allCurveSetDefin
         std::set<RifEclipseSummaryAddress> addressesFromSource;
 
         // Build case list
-        auto addresses = ensemble->calculateUnionOfSummaryAddresses();
+        auto addresses = ensemble->ensembleSummaryAddresses();
         addressesFromSource.insert(addresses.begin(), addresses.end());
 
         for (const auto& addressFromSource : addressesFromSource)
@@ -354,7 +354,7 @@ std::vector<RiaSummaryCurveDefinition> RiuSummaryCurveDefSelection::selection()
 
         if (ensemble)
         {
-            std::set<RifEclipseSummaryAddress> addressUnion = ensemble->calculateUnionOfSummaryAddresses();
+            std::set<RifEclipseSummaryAddress> addressUnion = ensemble->ensembleSummaryAddresses();
             for ( const auto& addr : selectedAddressesFromUi)
             {
                 if (addressUnion.count(addr))
@@ -978,7 +978,7 @@ std::set<RifEclipseSummaryAddress> RiuSummaryCurveDefSelection::findPossibleSumm
         }
         else if (currEnsemble)
         {
-            allAddresses = currEnsemble->calculateUnionOfSummaryAddresses();
+            allAddresses = currEnsemble->ensembleSummaryAddresses();
         }
 
         bool applySelections = identifierAndField == nullptr || (!isVectorField && controllingIdentifierAndField != nullptr);