diff --git a/include/openPMD/IO/ADIOS/ADIOS2File.hpp b/include/openPMD/IO/ADIOS/ADIOS2File.hpp
index d34cc8ebe5..fb596823ac 100644
--- a/include/openPMD/IO/ADIOS/ADIOS2File.hpp
+++ b/include/openPMD/IO/ADIOS/ADIOS2File.hpp
@@ -229,6 +229,10 @@ class ADIOS2File
      * on chosen ADIOS2 engine and can not be explicitly overridden by user.
      */
     bool optimizeAttributesStreaming = false;
+    /*
+     * Used for a number of BP5-specific optimizations. Written in getEngine().
+     */
+    bool m_is_bp5 = false;
 
     using ParsePreference = Parameter<Operation::OPEN_FILE>::ParsePreference;
     ParsePreference parsePreference = ParsePreference::UpFront;
diff --git a/src/IO/ADIOS/ADIOS2File.cpp b/src/IO/ADIOS/ADIOS2File.cpp
index 68d76b0088..d264a66a09 100644
--- a/src/IO/ADIOS/ADIOS2File.cpp
+++ b/src/IO/ADIOS/ADIOS2File.cpp
@@ -109,7 +109,9 @@ void WriteDataset::call(ADIOS2File &ba, detail::BufferedPut &bp)
                     std::nullopt,
                     ba.variables());
 
-                engine.Put(var, ptr);
+                auto do_defer =
+                    ba.m_is_bp5 ? adios2::Mode::Sync : adios2::Mode::Deferred;
+                engine.Put(var, ptr, do_defer);
             }
             else if constexpr (std::is_same_v<
                                    ptr_type,
@@ -180,7 +182,9 @@ struct RunUniquePtrPut
             bufferedPut.name,
             std::nullopt,
             ba.variables());
-        engine.Put(var, ptr);
+        auto do_defer =
+            ba.m_is_bp5 ? adios2::Mode::Sync : adios2::Mode::Deferred;
+        engine.Put(var, ptr, do_defer);
     }
 
     static constexpr char const *errorMsg = "RunUniquePtrPut";
@@ -976,6 +980,14 @@ adios2::Engine &ADIOS2File::getEngine()
         {
             throw std::runtime_error("[ADIOS2] Failed opening Engine.");
         }
+
+        m_is_bp5 = m_impl->realEngineType() == "bp5" ||
+            /* this second check should be sufficient, but we leave the
+               first check in as a safeguard against renamings in
+               ADIOS2. Also do a lowerCase transform since the docstring
+               of `Engine::Type()` claims that the return value is in
+               lowercase, but for BP5 this does not seem true. */
+            auxiliary::lowerCase(m_engine->Type()) == "bp5writer";
     }
     return m_engine.value();
 }
@@ -1096,13 +1108,7 @@ void ADIOS2File::flush_impl(ADIOS2FlushParams flushParams, bool writeLatePuts)
         {
         case FlushTarget::Disk:
         case FlushTarget::Disk_Override:
-            if (m_impl->realEngineType() == "bp5" ||
-                /* this second check should be sufficient, but we leave the
-                   first check in as a safeguard against renamings in
-                   ADIOS2. Also do a lowerCase transform since the docstring
-                   of `Engine::Type()` claims that the return value is in
-                   lowercase, but for BP5 this does not seem true. */
-                auxiliary::lowerCase(engine.Type()) == "bp5writer")
+            if (m_is_bp5)
             {
                 target = CleanedFlushTarget::Disk;
             }
@@ -1136,9 +1142,13 @@ void ADIOS2File::flush_impl(ADIOS2FlushParams flushParams, bool writeLatePuts)
             m_uniquePtrPuts.clear();
             m_updateSpans.clear();
             break;
-        case CleanedFlushTarget::Buffer:
-            engine.PerformPuts();
-            break;
+        case CleanedFlushTarget::Buffer: {
+            if (!m_is_bp5)
+            {
+                engine.PerformPuts();
+            }
+        }
+        break;
         case CleanedFlushTarget::Step:
             if (streamStatus != StreamStatus::DuringStep)
             {
@@ -1246,16 +1256,6 @@ AdvanceStatus ADIOS2File::advance(AdvanceMode mode)
         adios2::StepStatus adiosStatus{};
         auto &engine = getEngine();
 
-        auto check_bp5 = [&]() -> bool {
-            std::string engineType = engine.Type();
-            std::transform(
-                engineType.begin(),
-                engineType.end(),
-                engineType.begin(),
-                [](unsigned char c) { return std::tolower(c); });
-            return engineType == "bp5writer";
-        };
-
         if (engine.CurrentStep() == 0)
         {
             int max_steps_from_env =
@@ -1273,13 +1273,13 @@ AdvanceStatus ADIOS2File::advance(AdvanceMode mode)
 
         // Check some conditions on which to now cancel operation due to
         // unwieldy metadata sizes in BP5 with group encoding
-        if (this->m_impl->m_handler->m_encoding ==
+        if (m_is_bp5 &&
+            this->m_impl->m_handler->m_encoding ==
                 IterationEncoding::groupBased &&
             this->m_max_steps_bp5.has_value() &&
             engine.CurrentStep() >= *this->m_max_steps_bp5 &&
             (this->m_mode == adios2::Mode::Write ||
-             this->m_mode == adios2::Mode::Append) &&
-            check_bp5())
+             this->m_mode == adios2::Mode::Append))
         {
             throw error::OperationUnsupportedInBackend(
                 "ADIOS2",