Checking back in since new information came to light.
Although I agree with you that froggies would love to kill and eat fishies... My ACF doesn't bother any of my fish. It's living with about 40 other assorted Tetras/Danios. Is there something wrong with it?!
Your ACF sounds interesting and fun. I feel ripped off! Mine is slow, blind, and generally not very lively.
It's hard to say. ACF are all different (on some level). Danios and Tetras are pretty fast fish, maybe they're just too fast for him. I'm surprised he doesn't get lucky now and then though. Live bearers are very slow, they're easier prey for an ACF, in my opinion. With so many fish in the tank it may hide a lot, maybe it feels threatened a bit. Is your ACF young? They get bolder with age, froglets tend to hide more.
I have one ACF who likes to hide a lot, one who is very interactive with me and likes to be hand fed, and another who really enjoys hunting down fish and is very predatory (wild type).
It's actually kind of cool you can keep yours with fish. I've had no luck. My wild type ACF is so crazy and predatory I would find the fish hiding behind the filters and obviously stressed so I moved them to their own tank.
Honestly though I've seen all three go after fish, does your ACF even try? Generally they are most successful at night when fish become inactive and rest at the bottom of the aquarium.
I've never seen my ACF actually catch a fish, I've turned on the lights in the room and seen one in their mouths though!