Not sure if it made a difference but at least I know they’re set now. I’m a fan of the cardboard-deflector method, but when it pops out of the lip on the edge of the head without you realizing it...

The experience can best be described via this picture from the internet.

One of these days in a junkyard I’m going to pick up a stamped valve cover and just cut a slot in it for this sort of thing...

Works great when the cardboard actually stays positioned to direct the oil back into the head as opposed to down the side of it...

Sopped up probably a pint of oil from the floor when I was done. Good thing I topped it off before I started...