I've seen a lot of people agree with the belief that they eat better in smaller tubs. They feel more secure so when food comes along they're more willing to take it.

That said, at their sizes it's perfectly reasonable for them to slow down a little. I've heard of so many walls for snakes (mostly the 1000g wall) where they will slow down at that point. Just keep watching their weights so if they start losing too much you can go to the vet or do something else.

If they won't take live then I wouldn't worry about it until the weight loss gets bad. Then I'd maybe start looking into asf's, mice, scenting, etc.