Peebles;
I also shoot a chappy boss.... I find that if you have the anchor point ( such as you refer to it as your index finger knuckle )to far back that there is a tendency to drop your release arm elbow......... holding with the anchor you refer to I find myself haveing to really strain to get the release elbow to stay up and a straining uncomfortable shooting form is not condusive for me to good shooting... the elbow wants to naturally drop because it is more comfortable... but by useing the string as my reference by haveing the string contact the same place on my nose at full draw and with the release hand anchored on the side of the cheek just in front of the ear with my cheek bone ( I have high cheek bones )laying between my (fist knuckles) of the pinky finger and the ring finger that there is much more ease to keep the release arm elbow up.
Now with this kind of anchor due to your draw length you may have to lose the string loop or shoot with a straighter bow arm ... that is if you dont want to ajust your draw length.... but I would if it was me ajust the draw length to fit the anchor point and keep the string loop.... remember with a wrist strap release many will make your release hand sit farther back from the string due to the length of the release extension and head.... a release with the chappy boss will make your release hand sit closer to the string since it is a smaller hand held release with a shorter distance from the hand to the release head.