Yeah I am not sure what to tell you more than that some snakes are really particular- or as you said, become used to the enclosure size, environment they were used to being housed inside for the previous time. I have tried to upgrade my red tail but he only ever occupies as little of it as he can, so I wonder if I should just downgrade him again. Maybe house him in the previous enclosure for a week and try to feed him again, see if anything changes. If not, go from thereSorry I couldn't be anymore help.