Geronimo. You asked why sitting was your problem. There are 2 main reasons that cause lots of little things to happen.

FIRST: you lose your foundation. When standing you have the amazing strength of your legs to help you hold the bow. When you lose that you have to depend on your back to hold you upright and you lose all the stabilizing ability of your legs. Now you have to draw a bow and adjust it to try to settle a pin with all the foundation gone. You are down to arms alone. This causes an upward lifting motion of the shoulder and/or you lean backwards just to counteract what you lost by sitting. As soon as the release is touched this upward pull of the shoulder and/or this lean goes into motion and you hit high.

SECOND: When sitting you are facing the target more squarely than if you are standing with you toes and body facing 90deg. to the target. This shortens your draw more than you realize. You are also less able to hold the wt as mentioned above and tend to creep forward.So all this combined has you releasing at aspot more forward in the draw cycle and you hit high. Don't believe it? Try intentionally short drawing your bow or creep forward so that you are through the valley and starting back into the higher draw wt a little and release. See where your arrow hits. But be sure you have a safe background!!!

WHen shooting off your knees you will tend to get back to the perpendicular stance just like on your feet and you have your foundation back. You can completely draw and shoot much more like standing than sitting will allow.

One other question. I am assuming since you went on this type of hunt you used a rangefinder. If not you could also add misjudging yardage to animals you aren't used to seeing in terrain you aren't used to looking at. Give all this a try and see if it makes sense to you.

Man I am so sorry about your misses. Look on the bright side, now you have a good reason to go back! That would be my DREAM COME TRUE.

Dave