Another thing I noticed with my boy Cosmo...
He seems to be more eager to accept prey that's a bit cooler than what all my other snakes seem to like.
He's backed off a few times when the prey was really good and warm. This was back when he was still on pinkies, so since correcting I got to troubleshooting and wondered if the prey was actually starting to cook since they were tiny pinkies. I honestly don't know though. And that's just limited to my one snake.
Not sure if this helps you out at all, but I figured it was worth mentioning.