I used to play my bass behind my head at all times, some times with one hand strapped to the adjacent thigh, it was a style thing aswell, but i, like you found that my technique was being hampered by doing it, so i stopped....
I guess what i'm saying here is:
If you can't do it and you suspect the hight of your strap is at fault, then change it! what looks worse? Someone with a bass 2" higher than regulations stipulate or someone who can't play bass because they didn't want to carry it off the ground?
