I wouldn't say they are eating great and say you have a problem feeding. Just doesn't make sense.
As long as they are eating I wouldn't complain though.
If you knew the rat was to large why did you try to feed it?
If it were me I would keep feeding whatever they will eat and every once in awhile try a rat that is the appropriate size.
I have a few snakes that take a good amount of time before they start eating. That's a perk of using f/t.