Thanks Larp
An alternative, Version 4 is attached.
I thought there was a condition in the back trigger to say only try to repeat the back if the amount of previous backs matched is zero. By the time a selection that last trading at 100+ is now trading under 10 things are moving very fast so the first back may not be matched - that is why I did not originally choose "once per selection" for the back.
That is definitely in V4. I agree that choosing to lay all those above your threshold value "at SP" is more likely to get them matched (albeit that you cannot guarantee the odds) but it will be in the right vicinity normally. Remember some races can be dramatically delayed and prices can wander between the bet being placed and the start - but that is unlikely to dramatically affect the outcome of this strategy.
I would watch the back bet carefully. When doing things manually your brain subconsciously takes in a lot of data so whilst you may be watching for odds of 10 you may choose not to hedge (perhaps, for example, if the front runner is already at 1.03). The trigger does not apply these discretionary checks, which is both the strength and weakness of automating a strategy. It takes out the emotion - but, within the constraints of the API and the internet etc - applies the constraints rigorously in every situation.
Such further conditions can be added to the trigger if you can think of any that you would want to apply.
Good luck again and thanks for being patient - I hope it works better today.