The weather has improved here and I was able to take these test shots. One was without flash for reference and the other two were at 1/250 and 1/320 synch speed. The top photo was shot at 250th and the second at 320th.
Unfortunately, I can see any edge differences between the two shots. The rabbit in the second shot does seem better exposed, but that may be some extraneous factor. Am I missing something?