Absolutely agree that having externally accessible food bowls is best. This is great antecedent arrangement!… ie. you don’t have to put your hand in the cage. Many birds don’t like you putting your hands in the cage, which is why many modern cages are built with this facility.
Plus larger cages are usually better so that the bird has the space to get away from you and each other if necessary… thereby helping to reduce “aggressive” and/or “fearful” responses. Cage placement is certainly important. I don't think many birds would like to have human traffic passing them all the time. Having the cage against the wall or two walls gives more security, a place to retreat if wished. And if you can't provide a wall, a plain neutral coloured sheet over the back of the cage also works. Although this could encourage nesty behaviour...
By all means provide nesting materials or nest box, etc. and be aware the flip side can result in an increase in aggressive behaviour in some birds. So try it, but monitor it. As with any changes you make to behaviour, monitor the results. If something isn’t working, rethink, try something else.
All I am saying is by using observable behaviour rather than using labels, you are more likely to be able to understand and therefore deal with a problem behaviour.
Behaviour is a study of one – every bird is an individual. There will be species specific behaviours that are useful to know, but even these are workable. For example the dawn and dusk chorus is a natural behaviour. Yet a well known behaviour expert changed her Blue-fronted Amazon’s “dawn chorus” to singing songs/nursery rhymes. The bird chooses to sing the songs instead of screaming because there is LOADS more reinforcement for the singing. An animal always chooses to do the behaviour that gains most reinforcement – it is called the Premack Principle.
If you can identify the antecedent(s) and the consequence to a behaviour (and EVERY behaviour has them – some are maybe harder to spot but they are there), you have knowledge you can use to change that behaviour.