My experience in YM is that when I used smaller than 20, I would get whipped around on noise or on stop runs. If you can nail dead perfect entries, then perhaps you can use smaller stops, but with less liquidity ES, stops get run easier. Also I have a theory on rule of 20 that incorporates into YM trading, but that is a whole thing subject. What stop size are you using now ? My adivce to you is to trade just 1 contract and adjust stops to see what works for you best.