As I said Jonathan, I've been told that the above rules can be optimised so that hitting any url in the path I mentioned would run just one rex rule instead of a minimum of 3 currently. I have been told that by an nginx expert but what I have not been told is how to achieve it. I suspect it will be by nesting location {} constructs (is thsat possible) or by having more selective location {} constructs.

I want to start with as optimised a set of rewrite rules as possible.

Does this help any?