To bottom out the shoulder as you speak of really is easy.
1. First Go to a wall and stand a few inches past arm's length from the wall.
2. Nowlay your hand with the palm flat against the wall with your fingers pointing to the top of the wallwith your hand at your at shoulder heigth on the wall.
3. Standing with your feet together
( and they will be pointingdown range )
lean with all your weight on your hand that is laying flat against the wall.... while your face is pointing at the wall.

4. Stand in this position for as long as it is comfortable .... notice how if you roll your shoulder up into your chin while you are leaning against the wall it is very uncomfortable... now when you roll your shoulder down to where you can comfortabley lean against the wall for a long period of time you have achieved the bottomed out shoulder that will give you the bone on bone contact that will inable you to hold steadier and at full draw for longer periods of time.... thiscan also aid you to develop a optimum low wrist grip.