as you could see on many examples from korHarmonics indicator, the 121 pattern is often precise to the 1pip. This offers very small SL and big TP.
I am analysing the market in fractals, so i am not using fixed rule for SL like 113 or 127%. I am observe how market approaches the D point in the 121 pattern and place the SL accordingly, depending on the dynamics of this move. Sam Seiden appraoch with Supply/Demand zone is very good here. Anyway, fixed rule for SL will work also well.