OK, I should start off by saying I am not a huge fan of Divinity style surfaces and their emphasis on them, but I understand that they are going to be part of the game. Why don't we implement surfaces like how they are in the actual 5e game? Let's say you have a Wall of Thorns spell. The way that this game would handle it, is you take damage 1. When the spell is cast. 2. When you start your turn there. 3. When you move out of it. Do you see the problem here? In 5e, you take damage from Wall of Thorns when 1. When it is cast. 2. When you end your turn in it. 3. When you enter it for the first time on your turn. You also get saves to see if you take half damage every time. Please implement it like this. Right now, you take damage from firebolt 3 separate times and mostly cannot avoid it.
