Angelfish are cichlids (I know, obvious, but many forget this). They are very territorial, a trait that is part of their genetic makeup. No one is going to change this. Why some individuals are more aggressive than others, this can depend upon environmental conditions [they are not getting something they expect], but sometimes also individual fish just don't follow the norm exactly. Tank raising has nothing directly to do with this, it is genetic. We do know without doubt that the space (aquarium size) and the number in the group determine aggressiveness. In their habitat, the fish remain in groups of roughly 30, and as pairs form, the others just move out of their way. Placing them in a relatively small tank is not going to pay out.
A comment on the species...I've no idea what "longnose" refers to, but there are three species of freshwater angelfish. Pterophyllum scalare (Schultz, 1823), P. altum Pellegrin, 1903 and P. leopoldi (Goss, 1963). In 1998, Sven Kullander erected the subfamily Cichlasomatinae and moved the genus Pterophyllum into it. It is my understanding from Kullander (1998) that all varieties are derived from P. scalare.