Again, form comes down to
Personal shooting style is always based on the shooter's individual physical capabilities and limitations. Art P/2004
However, whether or not "squared" shoulders are correct for you, can be dependent upon, not only your individual physical characteristics, but such things as the type of release you use and the type and location of anchor you use.
When I shoot my compound, using a mechanical (wrist) release, my anchor is at my jaw line, my shoulders are squared, and the elbow of my draw-arm is level and directly inline with my shaft.
If I use a "T" release, I used a reversed hand and my anchor is near the corner of my mouth. My draw-shoulder is a bit higher because I now elevate my draw-arm (elbow) to keep my anchor rolled into my face. The same when I shoot with fingers.
As for the head position, I always slightly tilt my head inward, with very little twist, just enough to touch my anchor checks and align my string and sight pin, or eye to/along the shaft if shooting instinctively or gap.
I would think that anyone that uses a "string peep" would have to tilt his or her head inward. If you hold your head straight and upright, proper eye to sight alignment most likely will not be correct.