20 whitebait? Haha, jesus, that's a lot even for a big dat.
I have tried similar things such as dropping at either end, but haven't had much luck. In order for the bottom dwellers to get a share I need to just drops loads in all at once, so I probably overfeed a bit too. Before I had a jardini and snakeheads and pbass that would gobble everything super quick, and now just some greedy CA/SA cichlids.
Have you thought about using feeding sticks? I have two barramundi that basically hog all the food that gets thrown in, so for the slower fish, I use those little cane shish kebab sticks to target the fish that I want fed.