If you're putting the rat directly into the water that could be dulling some of the smell of the rat. That might lead to the slower strikes. I had a few beeps that had no problem eating wet rodents that way....
But now I have a few fussier eaters and I need to 'sous vide' them in hot water while in a baggie to lock that oh so wonderful smell inside. Lol.
Now that's fascinating! I'll have to try it next week and see if it changes anything.
Snakes are so weird! "My rat is too wet so I'm not gonna eat it." Gotta love'em anyway though.