Do-not look for % of profit that can be made on investment put in-to a trade, wrong way to go full-stop.
What you need to do ,is work out what the market will give you with the system you use to make profit , If i said to you i can take 1 point from the E-MINI sp each day and i invest X-amount ,The gain depends on the amount invested (x-amount of cars)With a $200,000 investment 1% whould be $2000 Thats 40 point gain with 1 (contract) to make $2000 or 2.5point gain with 16 (contract) to gain $2000 your investment whould be 16x(contract price) to make $2000. at the end of the day if you are a small investor just take what the market will give with the system you have...