I actually think you are on to something with not placing them back If they aren't eaten. I do the same except I have a cool down tank. I figure if the other rats smell the snake on a scared freaked out rat they may associate the smell of snake with something bad. Leading to rats that may bite the snake when being fed off. So what I do is If one or more isn't eaten I place it in a cool off tank for 24 hours to chill out and calm down and get the smell of snake off. I don't know if it really helps but I like the system.
Check out what's new on my website... www.Homegrownscales.com