Not often I disagree with Bob and this is something someone should easily test for themselves. However, I will say that for me, beyond any doubt, tucking the two middle fingers back is more stable than all fingers forward. The two outside fingers still have the same spread, so the front of the bridge is just as stable or too close to tell. However, those two middle fingers that might add a little stability going to the front, add a lot of stability going to the back.
Simple theory really, a larger and firmer foundation with the fingers curled back. Too those knuckles planted have more stability than fingertips on the table. I often drop my bridge on the table with all four fingers forward. Then I deliberately curl the center two back. This is a case where I wouldn't listen to me or even Bob though. Too easy to test for yourself. Set up a shot that is a little touchy, mark your spots, start shooting alternating each bridge and keep score. After twenty shots, which bridge made more balls for you?
This is an issue that may or may not be relevant, humans have widely varying finger lengths compared to their other fingers. The length of your fingers compared to each other may come into play here. May not, just a random thought as I went to hit enter!
Hu