Tuning is fine, we do them for weeks now with random numbers.
2/2/7, 2/3/7, 2/3/8. 2/3/10 depends who slacks and who doesnt cause it was summer.
They just get a bit easier with more people since if someone doesn do the mechanic the others can do it but will take more damage, as example Touch of Sargeras on Avatar, with 2/3/7 and up you want 3 people in each soak, 2 can still do it but will be left with 10-20% hp instead of 50%+, still daoble, more dangerous.
You just need to know your raid, 12 years of raid leading makes it easy to tell apart who not to trust ;p