Yeah, I don't think there is a magic formula for fitting all instances... but so far (played my new ranjah) up to lvl 20 in qeynos2, crushbone, kurns, and paludal... and with the values I gave, they seem to be hitting right about where eqlive was... a little softer at the beginning levels... but I always hated dying 20 times until my 1HS went up enough to land a hit
I think on mobs 47+ (i.e. - no longer Dire charmable), the formula should increase a bit more... I'll know for sure when I test those levels out!