pp, if you're taking Top fluc then you can look at Betfair's new SP option. You can set a Limit for the Starting price. I do it especially if I know I'll be out and not punting 'live' so I'll enter my bets with Limits in the morning. You may need a good estimate of what the odds will be to set your Limit, but for Mel/Syd races IAS normally have their odds first thing Saturday morning.
In UK races you could set Limits for Place bets as well.