Frontosa can be picky eaters, some even go into a funk if they really hate a certain food. Back when I used it from time to time-- 20 years ago and before-- mine didn't care much for Hikari. That said, some of them can be shy-- another topic-- and yours may also be avoiding you somewhat and eating some when you're not around. They often come around as they more get used to you, sometimes it takes a while.
Without writing an over 20 year Cyphotilapia feeding history here, mine currently get NLS, including one tank I'm feeding NLS Ultra Red, which I'm experimenting with and they seem to love-- it's not making them red, LOL. They also get occasional freeze dried treats, typically mysis shrimp, occasionally other freeze dried shrimps or freeze dried brine shrimp. (I quit frozen foods years ago.)
other points--
1) Cyphotilpaia are a lake fish, typically deeper water, not fond of too much water current. Contrary to what some forums say, Lake Tanganyika does have various currents in it, so fronts don't mind some current, just how much can vary, but some people find a little less = happier fronts.
2) I've kept groups of 1.5" fronts by themselves in 6ft tanks. They were not intimidated by tank size and did not have trouble finding food. If it smells properly like food, they quickly know there's food in the water and have no problem finding it, not that I've ever seen. In fact, think about it, small fronts in a big tank comes closer to the scale of their natural habitat in a huge lake, and resembles their habitat even more if you give them at least a couple of decent sized rocks on the bottom in a mostly open tank.