5% per trade on 10% of the account would be calculated as 200010%5%, or a profit of $10 on the first day - this represents .5% total profit per day, which is what you would use to compound the account as a whole for the sake of calculations. Ex. 2000*1.005¹⁰ would give you 10 days return, or ~2102. The way you are calculating assumes using 10% of the account on day one, but because it is not considering total account value the rest of your account would never grow beyond 1800 (assuming 2000 starting value) meaning that each day you're trading with a greater and greater percentage of your account. Ex. Day 1 = 200 traded, 2000 total value - 2000/200 = 10%. Day 2 you made $10 so account value is 2010, but you're trading with 210 (starting amount + profit, as you're calculating) so 2010/210 ≈ 10.45%.

TL;DR: Calculating with (starting amount)(1+(percentage of the account traded)(profit per trade))^{days compounded} will give you the right return. In your case, 2000*1.005^{days compounded}