The recent change to Fire Damage in the Orryx Patch has confused some players. There is a long explanation from the devs, followed by a couple of good summaries here: V 1.10 Question about fire damage - #22 by Valygar
To summarise:
- The Target takes impact damage from the delivery weapon used - which is 80 minus armour for a Dante and 20 minus armour from a Purification Grenade.
- The Target is immediately set on fire and takes 40 minus armour to each location.
- At the start of its next turn, the Target will take a further 40 minus armour to each location. However, if it moves off of the flaming tile, its burning status is instantly removed and will take no further damage.
- The tile will keep burning, reducing its damage by 10 until it burns out.
- Anyone or anything that moves into that tile takes burning damage to all locations and to its general HP equal to the current damage of the tile minus armour.
There seems to be a bug that if the target moves diagonally between two burning tiles, it will not take damage (because it did not technically enter either of the 2 burning tiles).
The thing to remember now is that a burning target no longer carries its flaming status with it. It will only take damage if it stays in, or moves into, a burning tile - and it will only take that damage once per turn, not from every tile it moves through (or at least that’s what my tests seem to show).
Hope that helps.