Ahhh, right. I think that makes everything clear now. So, I guess there are more archers who do that with their bow shoulder than there are archers who don't. It is very common. It seems like it happens all by itself,yes? If you push your shoulder forwards while standing as if to shoot, you will also find that you can pull it back again to where it started. In fact, if you push it forwards then bring it back and repeat that a few times you will start to feel where the shoulder should stay when you shoot. If you then try the same movements with your bow in your hand( strung) but don't hold the string,just the bow. You will find you can push or draw the shoulder back, at will. Next you can hold the string and do the same shoulder moves, just to get used to them.
The next stage can feel a bit odd so take this slowly. Try the same shoulder moves forwards and back while holding the bow and with a just a short draw on the string( 5cm or so.) As you get used to this, make sure both hands are at eye level and not down at chin level. Keep the drawing elbow up at eye level ,too.
The next stage is where you will start to learn how it feels , so again, take your time and don't go getting sore or bored. Just do a few and then have a break, unless you really want to continue. Following on from the earlier posture and with the bow arm pushing out and coming back, try to push and bring the shoulder back, then draw the bow part way back making sure the shoudler does stay back. You will have to work on that and you may not get it right first time, so don't think it won't ever work...it will.
What you need to have in your head, is the feeling that only the draw arm is working and the bow shoulder should feel stuck back. You have got used to pushing forwards at the shoulder, so now you have to get used to pulling it back instead. When you first start it may feel very odd. Try to imagine you are trying to get the bow shoulder down closer to you hip.( just don't lean over to get that feeling stand upright)
With a change of this sort it is a metter of getting better at the new form. The more you get sorted before you shoot for real , the better. When you do get as far as shooting the new way, shoot at close range so you don't suddenly go from doing exercses to shooting a round or long range. When you first shoot , you want to be getting the shoulder in the right place as often as possible. Shooting a rouns or long range, can take your mind off the work and it is so easy to fall back into the old ways you have got used to.