i never had problems with my bichirs not getting food, if they weren't getting enough of the sinking pellets then they would start to swim to the top and and get the floating pellets as well, one of my bichirs would straight up come and swim up on a group of pellets on the bottom and lay on them so that the cichlids wouldnt see them and then would eat them as it swam backwards and uncovered them as it ate the previous ones, it was pretty amusing to watch lol
but if yours is having trouble competing it might help to maybe feed the cichlids and then throw in some more sinking pellets after you turn all the lights off so they dont see them and the bichir can get a chance to find them