You’re welcome, and I’m no expert but I will share what I know.
Considering that your male is the couch potato type I would guess that is his biggest problem and it sounds like he is getting a lot to eat for an inactive snake. You just need to limit his intake however you see fit, without seeing exactly what he’s’ been eating and how big/healthy the rat fuzzies are, it’s pretty hard to judge. If your mice and rats fall within the average, chunky hopper mice and the average fuzzy rats fall within about the same percentage range with regard to fat content. Anything above or below the hopper mice/fuzzy rat category and rats generally contain a considerably higher percentage of fat by weight. Rats have a higher percentage of protein in all but the pink mouse category, where mice contain more protein up to about 3 grams in weight, about large pink size. Generally it’s considered that mice are a slightly more balanced diet than would be a steady diet of rats. A lot of people do use rats to put weight on their animals quickly and it works, but it doesn’t mean that it is healthy weight.
If it were my snake, initially I would maintain the same feeding interval and limit him to about half of what he has been eating if that were possible, say only one rat fuzzy instead of letting him eat his fill. If necessary I would stretch out his feeding schedule to something like every 7-10 days to limit his intake over a period of time. I would make him work a little for his meal and wait a little longer, long enough for him to get good and hungry and get up off of his BarcaLounger and roam his enclosure to burn off a little energy. Ultimately I would switch him back to mice when I ran out of rat fuzzies.
It sounds like you already know this, just keep in mind that thayeri aren’t designed to be extremely thick and bulky snakes and an overweight condition happens easily when restricted to an enclosure, the particular individual is inactive in general, and it loves to eat. A fat, lazy thayeri is an unhealthy animal that may not produce well, if at all.
Mike