i do something similar i rock it in the middle of the motion
if i go full length air come in and if i go all the way in air comes in so i kinda rock it in the middle ultra slowly
and after a small while lock it back up and generally get about 50% reound thats without drilling a hole in the cap. if i wanted more i think i would have to do that because getting any lower is just not possible for me yet i guess there is a knack to it and just takes practice