As you know
markfinn i use Bet Angel & i wouldn't be without it even if i didn't "trade" pre race sometimes,i'm not sure what your asking but it is possible to (say) just keep yoiur profit on a particular runner without "greening up" to create a bet to nothing on that horse & you can do the same on another runner in the same race and have two running for you as "bets to nothing"...or you can just take a field profit regardless of what may win the race....i have had plenty of pre race trades that have gone against me & i will take a loss overall on the race (before the off) that BetAngel equalises for me (reducing my liability on the horse i have traded).
I would strongly recommend that you watch some videos on crossover points & resistance points,that will help you understand what the market is doing much better.