Quite frankly your understanding of the film producer’s role is a little off. I am a member of a director’s guild, and there are much simpler ways of understanding what producer’s do.
The ‘executive producer’ is, simply put, the money behind the project. They keep an eye on the project from afar and rely on reports from producers and key artists.
The only real reason for an executive producer to get involved is if the show is going over budget or the product is looking bad.
Person Responsible for Production
The title producer usually refers to the most senior person responsible for production working near the shoot. They are involved in the hiring and firing of people and oversee how the budget of the film is being spent. You can think of this person as a Director’s fiscal conscience. An example of this would be something like a big crash scene with a Ferrari – the Producer would most likely determine how many Ferrari’s if any, the show could afford to crash to get the shot the director wants.
A co-producer is an individual with specialized knowledge required to make the film. For example, a production company might do all of its location work in London, England but then for financial reasons relocate to a city like San Diego to do all of their studio work. The producer that knows how much everything should cost in London is unlikely to know how much things should cost in San Diego so production would hire a co-producer to give them the added knowledge they would need accomplish the fiscal savings. Much of these savings are actually in the form of tax credits so accounting is a very big part of the job.
An associate producer is generally someone more loosely involved with production. You may hear jokes that they are the relatives that were somehow able to get jobs but this is not entirely fair. I generally find that they make good mediators when a dispute arises between a fiscal and creative choice.
Strangely, the producer’s creative input into a film project is significantly lessened when a director is brought on board. Though producers are ultimately responsible for the amount of money being spent on a film, they do not always get their way. I have seen many Producer’s open up the checkbook against their will. It is only so much you can do when you are halfway through a project, and high priced talent decide they want to do something a specific way – because unfortunately if someone has already invested $50m in a project what another $1m is to them? For proof of this read any budgetary article on the film Titanic.