Depending on R/R and setup I do not set a stop larger than 2% of portfolio. I trade over the shorter to medium time frame i.e. minutes out to a week or two.
Position sizing is also capped by what I can afford (metal capital and wealth capital) if I take a 50% step loss i.e. 9/11, take over bid etc. Of course its not infallible correlations etc.
Try a search Tech/a and others have covered this subject extensively in detail