I don't think the issue is your form; especially since you have successfully broadhead tuned. These split limb bows are VERY sensitive to relative limb deflections. All the forces generated during the draw and the shot come from the limbs...and each limb; although the same nominal size; has an actual measured deflection associated with it; and typically all 4 are different (and they need to be). The manufacturer determines based on the bows geometry where the stiffest limb of the 4 needs to be; 2nd stiffest, etc., etc. Reason for this is that cams are not symmetrical with the string and cables right in the middle; the cables are on one side and the string is on the other. And the cable guard applies side pressure to the cables and hence the cams.
So what does this all mean? It means that for each bow; the limbs have to be sequenced in a specific manner; and the relative deflections (differences between left and right) need to be a specific target. Since it would be impossible to manufacture and put the exact same limb in the exact same spot on every single bow; a range is specified. So as long as the bow is assembled with relative deflections that are within the specified range; they are considered in spec. BUT; each one is different.
So take 2 identical bows and look at limb deflections; Bow1 has limbs TL-142; TR-147, BL-144-146; and Bow 2 has TL-142,; TR-149, BL-144-; BR-147. Factory spread range is 5-7 on top and 2-3 on bottom. So Bow 1 is 5 top and 2 bottom; Bow2 is 7 top and 3 bottom. Both in spec.
This is where the bows start to differ; as far as why one bow tunes right down the middle and the next one has the arrow rest and sight maxed out to the left. Bow2 is much stiffer on the right side than Bow1; and is going to tune with the arrow rest more to the left than Bow1. So how does one fix this? By moving the cams on Bow2 towards to right; so as to redistribute the forces to compensate for the stiffer limbs. Or you could rearrange the limbs into a different sequence. Usually with these split limb bows; tuning with the arrow rest only works if its very close to start with. If not; you end up with the rest way off center to get a tune; which causes the issue with the sight.
I'm not saying that form, grip, etc. do not play a part...they do. BUT the limbs control all and will usually override all else if they are not sequenced correctly or if the deflection spreads (left to right) are not ideal. This was not nearly as big a deal in the past; because bow limbs were one piece solid with hardly no space between the cam and the limbs. Just grab hold of a cam on an older bow and try to twist it...VERY hard to do. Grab hold of the cam on you Faktor and force it to lean...you will see that it takes hardly no force at all; you can make it lean with just 2 fingers and about 1lb of force. This is why the limb deflections play such a big part of tuning on a split limb bow. If you shim that bow you can bring that arrow rest over. Hope this helps.