The loop does NOT CHANGE THE DRAW-LENGTH one iota...what the loop does change is the positioning of your ANCHOR POINT because you've moved your hand back farther away from the bowstring.
IF you were using a rope around the string release aid...then all you have to do to keep the same anchor and FEEL of the Draw-length is keep the distance of your knuckle from the string the same by adjusting the length of the d-loop to match how your hand positioning is with the rope around the string type of release aid.
We used to fine tune our "drawlength" adjustment by lengthening or shortening the release rope (and it changed the speed of the release slightly too, haha)...same principle...to get that exact positioning for the most solid and repeatable anchor point!
You cannot have a repeatable anchor point if your hand is floating back behind your ear somewhere in space....and this also affects your shooter's triangle and gets you all out of position.
I'd rather take the loss of a few fps and be ACCURATE and repeatable than have those FAST MISSES so common by people that insist on longer drawlengths than they should be shooting all for the sake of almighty SPEED.
But, people are different....it all depends upon whether you want repeatable and reliable ACCURACY...or you want mediocre scores, increase potential for injury, and staying way down in position on the leader boards...for SPEED sakes.
field14