I find that if I close my eyes at full draw, then open my peep eye without moving my head, and have someone move it up or down so that I get centered view without moving my head, I am as perfect as this old blind man will ever get.
As for my D-loop. When I use a trigger release I tie the loop above and below the nock. Experimenting with this method led me to tie a serving nock set above the nock so that I had a little room until the string was drawn.
When I use my BT, I tie my D-loop completely below the arrow nock, and tie a serving nock set above the nock. The reason some of us tie the D-loop completely below is because it gets the loop narrow. When we bring our hand back with the BT, we rotate our hand so the knuckles are against our face. A narrow loop twist easier without torquing the string as much.