Years ago I did some experimenting on myself, including increasing to gain weight, and at least for me hunger seems to mostly be a function of relative emptiness from recent maximum fullness.

Sounds odd, but let's say I filled my stomach to 90% of my total capacity, then a few hours later I've digested down to 45% capacity and that's when I get hungry. That's -50% of the last maximum. If I spend a week or two restricting what I ate to a maximum of 60% capacity, I'd only get hungry around 30%, also -50%. But with less total calories eaten.

(numbers made up just to give an idea what it felt like)