The more I play with the stats the more i realise that the price is the indicator of success.

This table looks at races (287,983) and uses TAB price with Fav. Rank to generate WSR's. The selected field size was 9 - 13 starters.

RANK..........1.............2............3........ .....4........
$2.0...........44.8%......XX........XX..........XX
$2.5...........34.1.........XX........XX.......... XX
$3.0...........28.7........29.9.......33.3........ .XX
$3.5...........23.7........23.3.......24.1........ .XX
$4.0...........20.0........20.2.......18.4........ 16.7
$4.5...........17.9........18.1.......17.6........ 19.3
$5.0...........15.6........14.9.......14.7........ 12.9

The average Aus Field is 11 (rounded .... I can't deal with 0.18 of a horse).

Doubtless it would be possible to correct either/both WSR and Price to BSP (I haven't looked).