I am pretty sure you have a lot more experience in these matters than me but I believe you are spot on from everything I have experienced/read. Unlike a baitfish or even shrimp etc...most crabs flee to the bottom and dig in to protect themselves relying on camouflage as their defense. I think it is in that regard that the merkin fly has been a successful pattern. Where I have more experience is with Stripers on the flats but most of us who sight fish have probably seen a fish spook when you over stripped a flounder/crab fly. Fish is expecting its prey to dig in and when itís right on top of it the prey tries to jump up and run. Just not natural.