Going to play devil's advocate here. How can we emphatically believe that a wide fish is unhealthily obese? AFAIK I haven't seen a BMI chart posted for fish.
All I can say is that when I've seen the same fish that we keep in aquaria in the wild, they were fatter and wider than the fattest fish I ever saw in captivity. As in no comparison whatsoever. So I tend to believe that in general even if we think we're overfeeding, we're not, not really anyhow. Yes it is true that as long as they see food they will eat food, so we can't use a "they'll stop eating when they're full" sort of thing to figure out how to throttle back the amounts, but the flip side is although they'll never really be "less" hungry, they can be "more" hungry and that can sometimes lead to aggression. So it's a fine line or a balancing act, maybe with some experimentation and observation you'll find the balance that works for you..