What I am suggesting will not resolve the main problem of why does the capper not work uniformly, but I keep a small hand capper and check the caps if I have a concern. I have found there is a style of bottle that is "in between size" (height) and the cap does not feel right when I use the bench...
DragonflyLady Brews I studied aquatic insects in school and liked the dragonflies, so I have used the nickname "Dragonflylady" for geocaching and my home brewing.