Average Fire Damage Calculations

[TheDragoon]

I've been trying to make a calculator that would calculate damages for Druid Elemental Skills for 1.10 but so far I haven't be able to figure out how the game is calculating the "burning" damage from when fire is sitting on the ground as a firewall (it's used in Firestorm, Molten Boulder, and Armageddon).

Little help here? :)