I'll re-read what you posted below and answer when I have more time but just quickly in response to the quote above what you want to do it work out all the permutations based on the win odds just prior to jump. Having every single permutation allows you to determine the place odds. The place odds though are going to depend on the "odds" shape of the race. Lots of long shots or lots of evenly priced horses will result in different place percentages (as it should).

I use the above approach semi-successfully at the moment on betfair. Its up over 150 units in profit so far based on backtesting and up 35.19 units in real time testing (not much $$$ on small bets though). I adjust for horses which win more then place and make slight adjustments for overbet/underbet. I then add a buffer for betting and a buffer for laying. Its surprising how many "value" place bets you end up with.