Here is some basic knowledge on
Zooxanthellae
I believe in feeding corals food in addition to light as I don't ever want a coral so hungry it eats its zooxanthellae. I have 2 dogs. I could probably keep both dogs alive with 25% less food than they are currently getting. In fact, I could probably do so for quite a while. Both Cheyenne and Cherokee are now fully grown. Would there be an impact if I did this during their growth phase. I don't know for sure----it's just a question. I have my suspicions though. For them to be healthy, they need proteins, lipids, carbohydrates, etc. What if I fed them the same amount of calories but decided they should have 25% less protein. Again, they would likely do fine for quite some time but it might not be optimal.
Don't even ask me what I think of the whole watts per gallon recommendations I see on the internet. Think about it. You have a corner tank that is 30" tall and has 5 watts per gallon. Your best friend has an 18" tall tank with 3 watts per gallon----in other words, the watts per gallon in this example are the same. You put a frag of the same mother colony on the floor of both tanks. All else being equal, which one grows fastest? Again, I don't know---it's just a question.
As a general rule, I hate general rules.
It is possible you are giving them enough "carbohydrates" to offset the "protein" shortage in my example. It's also possible you have great lighting for your tank and the fact that you feed also is making for some happy corals.