ianian,

Because Sydney and Melbourne have the best racing and the better class of horses, you can assume that the races are going to be harder to win with all these good horses competing for the bigger prizemoney so it is logical (?!) that there could be an edge to looking outside of these areas when we are talking about a mechanical system.

When it comes to the way I develop systems I look at filters that either eliminate horses or eliminate races, eliminating poor races is just as effective as eliminating poor horses and from a systems point of view, sometimes races form punters view as good betting races can actually be poor from a system point of view.

These are just my thoughts mate, I do quite well from the systems I develop but always test yourself as past results don't guarantee future profits. Good luck.

On the subject of pre-post there are some absolute gems to be had using the pre-post favourite as the starting filter.

Cheers,

Mat.