Agree with low light = bigger zoas/palys, but I wonder if spectrum matters too. I have 2 tanks with t5 bulbs. Run whites 4 hours and the blues 8 hours, but one has purple plus blue compared to blue only on the other. Both have large polyps, but the tank with a purple bulb has huge polyps.
The purple does have lower par, but I’m not sure if that’s the difference maker or not?