I am sure you will work it out, seems you are getting some progress. But, if in the water, when horizontal, the crotch strap seems tight, then that indicates the shoulder straps are pulling it so or the rig itself is lifting and pulling. What back plate are you sing?
I had to cut lower slots in my plate. I also leave the shoulder straps very loose. I cinch the waist strap but not the crotch or shoulders. Maybe you plate is too short or you need to lower the waist strap slots? Lowering your waist strap slots will raise the plate, loosening the shoulder straps and give more reach/distance between them to accommodate you. But, you will need to further lower the tank and possibly the cam bands.
My plates, keep in mind I am not a big guy, a skosh over 5-10 and shrinking, but look how big my shoulder strap loops are and my lowered waist band slots on the VDH plate. I never notice the crotch strap. But I am weight integrated also:
Maybe you need a bigger plate or further increase the shoulder strap loops. Let me put it another way, if in the water and horizontal and your crotch strap is so tight as to be uncomfortable, something is not right. The something is what is yet to be discovered. You should not need to do a Y (parachute style) crotch. It should not be tight to begin with. Your plate seems to have a happy home it wants to reside in, thus pulling the crotch too tight as you try to force/pull it lower, so maybe it is as simple as lowering your cam bands and tank further on the plate and relaxing the crotch strap?