The size has nothing to do with behaviour; putting this fish in with larger angelfish will not solve the problem, as it is natural behaviour. The two larger angelfish will either be dead quite soon, or if one of them should be dominant the troublemaker will soon be dead.
Angelfish are shoaling fish, which means they live in groups. These groups are smaller than the shoals of characins (tetras, etc) and similar, and usually somewhere around a dozen or two. In an aquarium, they need a group of at least five, and this means an aquarium which is at least four feet (120 cm) in length. But this may not be workable depending upon the individual fish. Some take their aggressiveness more seriously than others. Never have two, three or four together.
If you do have five (or more), there will likely be male and female and a pair may form and spawn. This can cause real problems and may require separation to avoid the death of subordinate fish. Point is, angelfish have special requirements and bring serious risks.