Make default pivot distance from head much closer to the chain head to reduce the chance of pruning limiting it's availability before it's completed. (#847)

Request 384 nodes per request instead of 200 since that's how many geth will allow returning.
Signed-off-by: Adrian Sutton <adrian.sutton@consensys.net>

ethereum/eth/src/main/java/tech/pegasys/pantheon/ethereum/eth/sync/SynchronizerConfiguration.java

@@ -23,11 +23,11 @@ import com.google.common.collect.Range;
 public class SynchronizerConfiguration {
 
   // TODO: Determine reasonable defaults here
-  public static final int DEFAULT_PIVOT_DISTANCE_FROM_HEAD = 500;
+  public static final int DEFAULT_PIVOT_DISTANCE_FROM_HEAD = 50;
   public static final float DEFAULT_FULL_VALIDATION_RATE = .1f;
   public static final int DEFAULT_FAST_SYNC_MINIMUM_PEERS = 5;
   private static final Duration DEFAULT_FAST_SYNC_MAXIMUM_PEER_WAIT_TIME = Duration.ofMinutes(5);
-  private static final int DEFAULT_WORLD_STATE_HASH_COUNT_PER_REQUEST = 200;
+  private static final int DEFAULT_WORLD_STATE_HASH_COUNT_PER_REQUEST = 384;
   private static final int DEFAULT_WORLD_STATE_REQUEST_PARALLELISM = 10;
 
   // Fast sync config