In addition to Eric1115's post, with the up and down movement, there is side to side deflection. When shooting in an unsupported position, the muzzle will track in a figure 8. Points of contact increase your stability (in theory). I choose ladder stands with rails, for this particular reason. Strong side elbow on a side rail, off hand supporting the fore end on the front rail with the back side, grasping the sling, over the rail. I set with my bottom backed into the back rest (or tree depending on the stand design) and lean at the waist into the rifle. Any way, that's the most stable and comfortable position that I have found for myself in a stand. It's the most like shooting off a bench as I can replicate in a tree. I use two styles of the off-hand position for shooting while stalking. The first, I try to use a tree, fence post, out building, anything to stabilize part of the shot. The second, is simply a very high mounted hasty sling with my off hand slid as close to the magazine box as possible, even grabbing the magazine box on a drop mag set up and tucking the elbow into my gut. My strong side has a firm and natural grip with the tricep horizontal to the ground (elbow straight out). I tend to position the butt higher on the shoulder than I normally would. Recoil is absorbed through the off hand and sling positioning, so the higher shoulder mount seems to be OK. Left leg forward, right back, bent slightly forward, in a good "shotgun" shooting position. Around here, it is very rare that one is afforded the opportunity to shoot from the prone, sitting, low or high kneeling positions, without being in an ambush position. Grass is waste to head high, or the underbrush too thick in the timber.