vixtor
Contributor
Don't use a crotch strap.
The crotch strap is part of the "magic" - it holds your rig fixed to your body, in a very stable position, no matter what are you doing (either floating at the surface, or being underwater horizontal, vertical, face-up or however else you wish). Without it the behaviour might resemble the one of a BCD, which floats around you, not very stable.
When i got my BP/W it took me a few dives to understand the importance of the crotch strap - initially I let it not tight enough (being scared it might bother me), but then I started to tighten it little by little, until it forced the shoulder straps to stay tightened, preventing any vertical movement of the backplate.