If you are basinf the win rate on margin then 10% of margin is terrific- for me the max is about 40%of my total account though I'm told I should trade bigger.
http://optionsinvesting.co.uk/trade145-week-ending-16-august-dont-panic/?fbclid=IwAR2HYIvPoYCTeVtj8ROu_Pp9Ekp185v6VHZHF0x6dlu5k5wCtcTBjnTCyYI