shooting from a sitting position is tough if your draw length is too long.....and to be honest, most are.

I am disabled and NEVER stand up. My legs don't work well enough to trust them. I never missed a shot in 14yrs but I practiced sitting and had my bow tuned to that. The key for both sitting and standing is be sure you are full draw and against the wall. If you creep, you miss, usually high and left if you are right handed.