Here you go... the difference was larger than i remembered, actually. Sry for the big pics, but since they were for reference I left them large.
The main difference is the width of the grip at the top. The smallest one has a severe flat dip, the medium is gradually sloped, and the large is just...well, huge. The end result - for me - is that the difference between small and medium is where my finger hits the trigger. For small, it's the joint. For medium, it's the finger pad. (I use the medium, and i have small hands).
It is now clear to me that I got the mid-sized backstrap on the AD-date I got from Florida. There were no others included and nothing but the second magazine. The question becomes; are the backstraps the same for the old frame as well as the new. I want to order replacement straps, manual, and whatever other items that were missing. What else should I be asking for?