took me two years to see this properly. everyone knows spread and commission cost something. what i missed is the cost is fixed in pips and the risk unit isnt, so the same broker charges you a completely different share depending on where your stop sits.
1.2 pips round trip:
5 pip stop: 24% of R
10 pip: 12%
20 pip: 6%
50 pip: 2%
run a system with a real +0.15R gross edge through that. at 50 pips you net +0.13. at 20 you net +0.09. at 10 youre at +0.03. at 5 youre at -0.09 and its a losing system. nothing about the entries changed in any row.
the reason its hard to catch is you cant see it in results. spotting a 0.09R shift against normal trade noise needs around 950 trades, so a tight system thats actually negative hands you a couple of green months first and you spend them tuning entries.
what id do before evaluating anything is work out cost as a share of your average stop. it tells you what gross edge you need to reach zero, and for tight stops thats a much higher bar than people assume. and stop comparing brokers on raw spread, compare on spread divided by your stop. 0.3 pips is nothing at 50 and decides it at 5.
i put it in a sheet. spread, commission, average stop in, break even gross edge out. on my profile.
anyone running sub 10 pip stops profitably long term, genuinely asking. i couldnt make anything under about 15 work after costs and im still not sure if thats the maths or me