Michaelg, here are some number to assist you.

Using the following rules ONLY

a) Not 1st or 2nd up
b) Min 9 prev. starts
c) Placed 7th or worse last start

produces 8.2% winners broken down as follows:-

AAP Price ..... %
1.1 - 6 ..... 4.2%
6.1 - 11 ... 2.3%
11.1 - 16 .. 0.8%
16.1 - 21 .. 0.5%
21.1 - 26 .. 0.1%
26.1 - 31 .. 0.1%
31.1 - 36 .. 0.1%
36.1+ ...... 0.1%

The price seems to be a very good guide :-)

Sample size 186k races 2m neddies.