Their is a good chance your draw is too long.A seated positions has to have a bow that fits you to be made easily but if the bow is right can be executed exactly the same as a standing shot.I will almost always shoot a deer from a seated position and prefer it in a stand,I am more comfortable like that when hanging on the side of a tree.I do practice that way and shoot a few tough man shoots,where you might have too sit on the ground and lean out,those require equipment that is right and a level.

Poundage is another issue,if you can't sit in a chair and raise your legs and still draw the bow,then the poundage is most likely too high.

The draw would be my guess.

Just some food for thought.