position sizing based on R (%of risk) when you need it fast

When I enter an order I set the stop loss technically and always have the same % of risk, and calculate the size based on that.

On the order window in cTrader, when I change % of risk the SL is moved, and I can't have that! I have to manually change the position size and by trial and error get to my number . It takes time, not really too much time but I trade the 1 min., I often don't have that time. On QuickTrade it's not possible at all. I downloaded an algo for position sizing, which works only with a fixed amount of pips for SL, so if I want to tailor the SL I can get hanged.

Suggestions? are there any algos that can do that? it shouldn't be complicated, is there anyone else with the same problem?