MG, just going over your calcs and I can't get it to balance. Lets say your bank is $500. 20% of bank = $100 liability. Median price of lays is $75, therefore stake for $100 liability is $1.33 less 6.5% = $1.25 nett. multiply by no. of winning bets 234 = $292.50 less one loss $100 = Nett profit $192.50. That's great, but you said your bank increased by 70% which is $350! Sure its not half that 38.5% or have I missed something. Still a good result though!
Cheers
RP