@DavidA I am by no means an expert, I’ve been doing this for a couple of months, but have managed some decent results.
the big change for me was having a set lay amount that I use for either placing a bet to attain a bonus or turning over a bonus bet.
i always have an amount that is an underlay, so usually in the 40-45 dollar mark, that way I get a small profit if the horse wins as well.
when turning over bonus bets I have an underlay that gets me a 70-75% return. Yes I can get more, but since this is an underlay have had some big Booms as when the horse wins you can make a good profit.
howver this method has eased my stress and has enable me to put as close to jump time as possible.