I've been testing something similar with TAB no 1 $11+ with a $30 liability (minimum SP amount) which has come up with the following:

There were 40299 horse form lines in the database at this point in time. We update when we get time.

There were 1508 selections for the System
There were 1451 which Lost (did not win race) for the System for a strike rate of 96.22%
You had to pay out $1230.50 but brought in $1432.6 after 5% commission. This means a Profit or loss of $202.1 or a percentage profit/loss of 13.4%

Test Another System

The Rules used were : WinPriceLay >= 11 and horseNumber = 1

Unfortunately every time I try it a horse wins and I'm $30 in the hole while maybe only making 50c to $2 at a time for the losing horses (winning lays).

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I've found this backing one with only 2 rules that looks good in theory but may go a long time between drinks:- Barriers 1 & 2 only, 1600m and above:

There were 40299 horse form lines in the database at this point in time. We update when we get time.

There were 1925 selections for the System
There were 222 Winners for the System for a strike rate of 11.53%
There were $2318.36 returned for WIN (after 5% commission) which means a Profit or loss of $393.36 or a percentage profit/loss of 20.43%

Test Another System

The Rules used were : barrier >= 1 and barrier <=2 and distance >= 1600