I use the "clip" style false transfer quite a bit, the one described in Williamsons Wonders and used as a middle step by Kainoa for getting into Edge Grip where the coin ends up clipped between the middle finger and index. Due to the nature of the move, the index finger straightens while the middle finger curls and therefore, the index finger tends to "pop" a little when the transfer is made. I'm interested to know if anyone has played around with minimizing this and the results? Keeping the thumb and index touching seems to help somewhat. Any other ideas?

By “pop” are you meaning the tip of the index finger moves outward? In that, it is ostensibly longer in appearance than when it initiated the movement. Regardless, the move got me has always existed in the realm of the larger motion covers the smaller. The retention of vision or the distraction of the apparent take of the coin far out weighs any specific movement of the index finger.

Actually, as far as I know that snap back technique was created by Al Schneider. I based my ROPS technique on this as well.