Question about corpse level and zone level

So, im playing cremation+unearth, my damage comes mainly from corpse life
and corpse life comes from corpse level, my POB tells me to get as high CORPSE LEVEL as i can meaning high level unearth by any means
but i saw a post where it said something about corpse level cant be bigger than the zone level (like monster area level)
so, why should i invest hundreds of divines to get unearth to level 30+ to get corpse level 100 if the biggest area level is... 84 i think?
is corpse level really limited to area level? should i just stop at corpse level 84 then?