Herald of ash support

Hi, im currently using Herald od Ash supported by reduced mana, increased burning damage and fire penetration. Im wondering if switching fire penetration for elemental proliferation is a good idea?

I dont know how many mobs have fire resistance and its crucial to decide how valuable fire penetration is for me.

One more idea is switching it for increased area of effect but i dont know if it will give me more in terms of heralds effect radius than EP?

Ele prolif is by far the better choice. Fire pen is worthless with HoA since it does not effect the burn.

edit: of course this is assuming you are not running a mechanic that will be destroying corpses like pyre ring. It runs alright with pyre but I find that I am better off using the mana reserve for something else, generally.