Elemental damage scales with the specific elemental skill if it scales the damage. If you don't have such skill learned, the damage stays on the basic damage level. So if I'm not mistaken, it depends on the character who set it ablaze, if I'm not mistaken. But not every environmental comes from a character, some happen indirectly through different effects. Sometimes it is hard to tell who exactly caused it.
Not sure, what the first part of the question means. If you dash you move faster and therefore you have less steps to take, so less contact to the ground?
