18 is where you double your money on a 1.04 bet all up. So to round it out to make it easier for maths I chose 20. So there is a reason. Its not magical. There is logic behind the decision.

You could go 40 or more if you wished but you have to choose some point so the double up point was chosen.

You go less if you want. At some point you need to choose the cut off point and weigh the risk vs the reward.

You shouldn't dismiss ideas because you don't like them unless you have results which show it doesn't work. The rules are very simple and anyone can backtest them through betfairs results service or could test them live.

Just because you and 95% of other punters don't like it, there are the few people which will like the ideas and will at least give them a go.

As I said if someone can show me figures which contradict my findings then I am happy to look over them and see where I got something wrong.