Moeee,
you being an avid greyhound follower will understand, when betting with the TAB's, pool size counts for everything in greyhound racing.

Trifectas being a good example of how pool size effects dividends for greyhound racing.
take this example,
I divide my trifecta database into 3 equal sizes based on the size of the pools

The 3rd with the highest pool sizes the median dividend is 173.45
The middle 3rd the median dividend is 163.30
The remaining 3rd with the lowest pool sizes is 156.20

all that might not mean to much to most punters, but just knowing the pool sizes can change your profit from a slight loss to a nice return, just in the above example.

Now using your example of that even money maiden racing on a skinny pool day, as compared to an even money maiden dog running on an golden Easter egg holiday crowd bumper pool day, you don't need to be a rocket scientist to understand what is going on

Doesn't answer your question directly, but for wagering you need to know your pool sizes first an foremost. In fact that is a major requirement for any database