Here’s another question that came into this blog recently: “Coach, any tip on aligning your stance with the target face. My kid always thinks he is standing right on line with the target but actually the target is behind his back.”
One thing you might try is to have him lay an arrow down at his position on the shooting line that points to a spot directly under the target center (any old arrow will do and do not do it for him, have him do it). Then his stance is aligned to the arrow. Doing this for a while leads to the ability to imagine such an arrow laying on the line and aligning his feet to it.
Basically, if he shoots from the same foot position for long enough his body will only feel “normal” if his feet are in the right place. If his feet are misplaced, he will have to swivel around to get aimed at the target and that will feel “odd.” This body awareness leads to adopting the same stance over and over, but only once the archer’s body is informed of the desire to have it so. I take particular pains to establish my shooting position the first couple of trips to the shooting line every time I shoot.
And do not assume that this should be “easy.” When shooting indoors I love to see a shooting floor that has been tiled (tiles here are typically 12˝ x 12˝ and made of something like vinyl). This creates a grid of lines many of which lead straight to the targets at the other end of the range. I use these straight lines as a starting point to build my stances (stances because they are different for recurve and compound).
Now, which stance of the myriad possibilities he will end up with is another question, but the primary need for stances is that they can be found consistently and to do that some such ability to orient to the target is needed. You can see the same effort in professional golfers standing behind their golf balls and eying a line to their target, some even swing their arms along that line or hold up the shaft of the club in hand it help them “see” it.