Woof,

Having now spent some time looking at z scores and their alleged relevance to team ratings I still have more work to do. However I'm convinced you're barking up the wrong tree.

The idea of taking the mean and stddev of a horse's past performance ratings is nonsense. For starters, typically performances peak after a number of runs into a campaign so your method would overrate 1st ups and those short of their peak distance range.

As for Techform (published freely on UNiTAB) which gives their favourite 100 in all races there is no sane way you can average a horse's Techform past performances. Like it or not you have little choice but to collate Techform differences with relative win chances, as I outlined.