Body/foot position backside

[wjp]

Something I've noticed lately is my backside feels very 'stiff' whereas from frontside is silky smooth and 'free'. Also lately I've been on my backside and finding that I'm starting to go down the line, but come out of the top of the wave and it passes by and by the time I realize this is happening I can't make amends.
I'm suspecting my body/feet position on the board - should it be any different that frontside? I'm also wondering if I need to generate more speed from the drop in, going into to a solid bottom turn (this doesn't happen too well on frontside) and hence no having the speed to keep the wave with me.

Any ideas/tips?
thanks