I'm sorry. Until this thread I've never even heard of "thumb rub".
I shoot lots of magnum loads - never happened to me.
I teach a lot of new shooters and I've never seen one of them do it.
BTW - I don't have small hands either - I have "man hands" - With a tip of the hat to Jerry Seinfeld.
Let's eat Grandma.
Let's eat, Grandma.
Commas save lives...