My Dad always hunted standing up said you can't shoot well when sitting. You could see where he had been because the first thing he did was clear everything away from where he was standing.
Degabe,
I have heard some folks say that they do shoot better standing "BUT" I myself have shot better while sitting down . Now that could be because I hold my bow to my left side and cant the bow as I draw and shoot. I shoot both standing and sitting but practice a lot sitting cause I mainly hunt the ground and stay seated when deer approach.
It isn't something everyone can do that's for sure but "If" you can shoot better standing then sitting then I would say stay with what works best for you.
For me it's sitting I must admit.