diff --git a/src/test/java/htsjdk/samtools/seekablestream/SeekableStreamGZIPinputStreamIntegrationTest.java b/src/test/java/htsjdk/samtools/seekablestream/SeekableStreamGZIPinputStreamIntegrationTest.java
index 6ef70f08e1..266fc86dce 100644
--- a/src/test/java/htsjdk/samtools/seekablestream/SeekableStreamGZIPinputStreamIntegrationTest.java
+++ b/src/test/java/htsjdk/samtools/seekablestream/SeekableStreamGZIPinputStreamIntegrationTest.java
@@ -111,8 +111,10 @@ private static String generateRandomString(final int length) {
     @DataProvider
     public Iterator<Object[]> compressedVcfsToTest() throws Exception {
         final List<Object[]> data = new ArrayList<>();
-        final int nSmallRecords = 1000000;
-        for (int firstRecordLength = 1000; firstRecordLength <= 10000; firstRecordLength+=1000) {
+        // 100K records is sufficient to exercise multi-block BGZF boundaries and detect the
+        // GZIPInputStream available() bug. 5 first-record-length variants cover the range.
+        final int nSmallRecords = 100_000;
+        for (int firstRecordLength = 1000; firstRecordLength <= 9000; firstRecordLength += 2000) {
             data.add(new Object[]{createBgzipVcfsWithVariableSize(firstRecordLength, nSmallRecords), nSmallRecords+1});
         }
         return data.iterator();
diff --git a/src/test/java/htsjdk/variant/bcf2/BCF2EncoderDecoderUnitTest.java b/src/test/java/htsjdk/variant/bcf2/BCF2EncoderDecoderUnitTest.java
index c7ade0d28d..841d6d0ee4 100644
--- a/src/test/java/htsjdk/variant/bcf2/BCF2EncoderDecoderUnitTest.java
+++ b/src/test/java/htsjdk/variant/bcf2/BCF2EncoderDecoderUnitTest.java
@@ -120,24 +120,18 @@ public void before() {
             primitives.add(new BCF2TypedValue(null, type));
         }
 
+        // One representative per type plus one null per non-CHAR type. Reducing from 17 to 9
+        // values cuts the 3-way cartesian product from 4913 to 729 test sequences while still
+        // covering all type combinations and null handling.
         forCombinations.add(new BCF2TypedValue(10, BCF2Type.INT8));
-        forCombinations.add(new BCF2TypedValue(100, BCF2Type.INT8));
-        forCombinations.add(new BCF2TypedValue(-100, BCF2Type.INT8));
-        forCombinations.add(new BCF2TypedValue(-128, BCF2Type.INT16));    // first value in range
-        forCombinations.add(new BCF2TypedValue( 128, BCF2Type.INT16));    // first value in range
-        forCombinations.add(new BCF2TypedValue(-100000, BCF2Type.INT32));
+        forCombinations.add(new BCF2TypedValue(-128, BCF2Type.INT16));
         forCombinations.add(new BCF2TypedValue(100000, BCF2Type.INT32));
-        forCombinations.add(new BCF2TypedValue(0.0, BCF2Type.FLOAT));
         forCombinations.add(new BCF2TypedValue(1.23e6, BCF2Type.FLOAT));
-        forCombinations.add(new BCF2TypedValue(-1.23e6, BCF2Type.FLOAT));
-        forCombinations.add(new BCF2TypedValue("S", BCF2Type.CHAR));
         forCombinations.add(new BCF2TypedValue("ABCDEFGHIJKLMNOPQRSTUVWXYZ", BCF2Type.CHAR));
-        forCombinations.add(new BCF2TypedValue("ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZ", BCF2Type.CHAR));
-
-        // missing values
-        for ( BCF2Type type : BCF2Type.values() ) {
-            forCombinations.add(new BCF2TypedValue(null, type));
-        }
+        forCombinations.add(new BCF2TypedValue(null, BCF2Type.INT8));
+        forCombinations.add(new BCF2TypedValue(null, BCF2Type.INT16));
+        forCombinations.add(new BCF2TypedValue(null, BCF2Type.INT32));
+        forCombinations.add(new BCF2TypedValue(null, BCF2Type.FLOAT));
     }
 
     // --------------------------------------------------------------------------------