Yesterday, while wandering around my club, I tried a shot sitting down. It was about 6” high, which is higher than I would expect to miss at that distance. In trying to figure out why that happened, it occurred to me that most of my attention had been focused on how different things felt drawing the bow sitting down rather than the actual steps in my shot sequence. I tried it again, but this time I purposely focused on my shot sequence and particularly on my sight picture when it came time to aim. The second shot was within the normal 2-3” accuracy range I have at that distance. But this made me think that if I intended to shoot from a ground blind in the near future I should spend a lot more time shooting under the conditions of the hunt, like sitting down, so I would feel comfortable and not be distracted by the differences.
There is no reason why you should shoot any differently sitting down than you do standing up, unless you have some kind of disability that only comes into play when you are sitting down. I'm sure that if you practice shooting sitting down enough times, and focus on your shot process, you'll figure it out. Probably some common error that would cause a high shot when standing up, like a drifting bow arm or inattention to your sight picture.