If you want to get super-realistic about it, let's look at the amount of time spent on/in the surface/cloud. We can't just use turns straight-up, because you can spend a portion of a turn within the area, and a portion of the turn out; we need fractional turns.
We don't know what a turn represents. A turn could literally equal 5 seconds. How many actions you perform in that 5 second period shouldn't have anything to do with how much damage you take from being in a fire. You're still only standing in the fire for 5 seconds whether you spend that 5 seconds imitating a statue or doing the macarena. It's 5 seconds of fire damage either way, and since (in this example) 5 seconds = 1 turn and the damage is (example) 10 fire damage per turn, then it's 10 damage per turn. It does not go up to 10 damage per macarena movement done within that 5 second window.
Let's say it's burning ground, and you have 10 AP for the turn. If you use all 10 of that AP on the burning ground, then you should take a full turn's worth of burning ground damage. The same is true if you spent 8 of your 10 AP then passed the 2; you were still in the burning ground for eight eighths of your turn.
Now if you left during the turn, let's say 5AP in and 5AP out, then you should take half that damage. Things get complicated if you spend 5AP in, 3AP out, and 2AP sent to the next turn; you should take 5/8 of a turn of damage, but as you're walking off you only naturally take the half-a-turn damage, so the game would need to add 1/8 when you pass the turn, even though you're off the burning ground already.
This is all moot since the game appears to apply the fire damage at the start of each character's turn, before they can spend any action points. In other words, your turn starts, you take 10 fire damage, and then you spend 2 out of your 8 AP moving out of the fire.. you still took the 10 fire damage already. I never said I had an issue with this.
You never actually explained why, in your opinion, I'm "wrong". That would be like me ending my post with
"TL;DR: Jello should have more flavors."
