I wouldnt worry about them swimming at the top but I would worry about them eating from the top. The problem with eating from the top is great if they take in a pellet or pellets and are fine...but if they take in air while trying to get the pellet off the surface then you will have a problem its safest not to feed any foods that float or stay on the surface. Keep in mind the aro's will grow much quicker then the front's will, do you plan to keep them? Just remember at full growns size you need to be able to house all of these fish. Personally I would keep your front tank just what it is... a front tank and if you feel the need to buy other fish for it, stick with africans, but that of course is imo.