Please see the trigger file attached.
There are 3 sample triggers in it, each laying on a horse with a particular rank (1st, 2nd or 3rd fav), with a particular size of bet, depending on the pattern in the name of the race.
See the constants you can use to adjust the settings of your triggers. To add more patterns, just add more constants and triggers and edit the conditions of the new triggers as appropriate.
Don't forget to test the triggers in Test Mode.