It could be worth looking at those later races to see whats going on, & rather than stopping at a fixed profit, it may pay to stop a race number X at each venue.

A system is a winner if it comes out ahead according to the rules. Stop at a winner is a system if that is the system rules. However stop at a loss or profit is money management or a staking plan. If a system does not produce a positive result on its own merit,then it is a loser. It might be today, it might be next week or even next year. Thus if you have a winning system then money management can help. If not then it will inevitally fail. However there are people that make money out of money management but that is more than stopping when in front. If you are risk adverse then stopping when in front may be a winner but do not regret what was left on the table. The only real way is to test and record the progress and make up your mind accordingly. Your system may work good on the early races and fail on the later which should form part of the testing. Beton