You've pretty much just repeated what I already said.Quote from 1a2b3cppp:
Futures trading doesn't always involve taking profit in percentage.
Half the time you lose 5 points. Half the time you gain 5 points. You're back where you started from (not including commissions).
If you have a breakeven system, using a fixed bet size gets you nowhere on average and using a fractional bet size actually loses you ground in the long run.
So the system has to be tweaked or replaced to get a new system with positive expectation for a fixed bet size, then you can apply Kelly sizing for optimal geometric growth, or some other sizing strategy if you have another utility function in mind.
It only takes a week or less of hacking away to figure out if you have something worthwhile or not.