Congrats on making some profits mate. Good work! Obviously we ideally want to extract as much profit as possible from matched betting, but it does all depend on which events are on and how tight the odds are between the bookie and the exchange. 66% is not bad, although aiming for 70%+ is always best.
Sometimes one just has to be extremely patient to get close odds to maximise the bonus bet. Like events with odds to back and lay of 5 / 5.1 etc are good for bonus bets.
Keep it u and give us a shout if you ever have any queries!