Hi Michael
Heres an idea that can work well on its day with half the O/L of your example.

Use some of your exsisting rules
. 11 runners or less

. Must have a $3.10+Fav in pre-post

.Divide the field size by 2 rounded up
e.g. 11 / 2 = 6

.What ever that figure comes to, that's how many horses we target using the pre-post market for the selections in name order as they appear in
pre post market.
e.g. Target the first 6 horses from a field of 11 in the pre post market.

Cheers.

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Cheers.