Hello! Your triggers are ready please see the attached file.
I had to add another milestone (so to say) to your strategy. Since you are assuming that it first reaches half SP, then keeps falling down, then turns around and start growing again, you need to specify how low it must fall before you want to start looking for the upward movement. Otherwise technically it can green up as soon as it falls to SP/2 - 1 ticks and then grows one tick back, if you see what I mean. So use the trigger_perc inside the file to set that limit.
There is a placeholder trigger for backing the favourite at SP. You didn't specify which horse you will be backing. If you are doing it manually, then just remove this trigger, otherwise choose the selection you want to back on.
Make sure you have tested the triggers in test mode.