Maybe it should be turned around so that standing does more damage and running functions as if you are on one of those "walk barefoot across coals" kinds of events, and it works - and you run over the coals quickly...
This was my first thought as well.
If we actually want to go all realistic about this, the characters shouldn't spend too many running steps getting out of the burning surface. People in real life don't run in half-meter steps like the imbeciles in the game. Especially if something under your feet is burning. You take big leaps of two meters maybe.
I think a better way out of this would've been to intensify the burning/poisoning the longer you spend in the surface or cloud, instead of just keeping the same crappy mechanic and reducing the damage taken by moving. Then maybe I would have interesting tactical choices like "The longer I stay put here, the more damage I'll take. But I might be able to use this turn to kill that baddie. Maybe I can try shooting once and then moving a bit to the side... But if I miss, he attacks me and I still take more damage from the surface..."
