The fire surface ticks damage twice - once on impact, again at the start of the enemy turn, no saving throw. That's 2-8 more damage on a single target beyond whatever the 1d6 of the initial hit and 1d4 from the burning status do.
As far as I can tell the damage goes as follows: firebolt hits or misses dealing 1d6 or 0 damage, the area under the target is set on fire. The target receives the "Burning" condition, which deal 1d4 damage immediately, and one more time during the targets next turn, after which the "Burning" condition is gone. If the target moves through a fire surface the burning condition is re-applied. If the target does not move and stands still in a fire the "Burning" condition is not applied.
The enemies don't have to move through that burning area. If you managed to snipe 2 goblins standing next to each other - good on you, that feels good to me.
From every single experience I've had with my numerous uses of Firebolt thus far, it ticks a lot more. Firebolt misses and still applies burning (on an attack that should have done literally nothing to the enemy), which is 1d4 damage right away, then at the start of their turn it ticks off another 1d4 damage, then they take yet another 1d4 damage whether they move out of the fire surface or not. In fact, depending on the size of the fire surface, I've seen it tick off 2 or 3 times just from the surface alone. And burning does not go away after that one turn as far as I can tell, it stays for at least 2 turns. Meaning that, if you get really lucky on the burn damage rolls, you can get a max of 12 damage just from those 3 burn damage ticks which is more than the 1d10 damage firebolt has in the 5e ruleset, not even taking into account the 1d6 damage it can cause if it hits. That's pretty OP.
Not to mention, burning and fire surfaces completely ignore AC, meaning it's not a hit or miss on damaging the enemy, it will always damage them no matter how high their AC is. The way this is set up right now basically means that the way to win literally any fight in the EA is to just toss out a bunch of grease or flammable barrels, and then use a single firebolt. No more moves needed, you win with your giant lake of fire. Or if you feel inclined to watch your warrior hack people to pieces, just make a bunch of acid areas and watch them go to work on their now significantly easier to hit targets. Wanna watch people slip and fall prone constantly? Get some water or blood and hit it with a Ray of Frost.
The point here is cantrips have been made stupidly OP for no reason whatsoever. The firebolt cantrip could be fixed by removing the fire surface and making it only tick off burn damage at the start of the burning persons turn, not instantly as well. The Ray of Frost cantrip can be fixed by removing it's ability to just knock people prone flat out, and either removing the ice surface or making it so the ice surface doesn't have a chance to knock people prone either. Having it slow them down on top of creating a rough terrain area which slows them down as full is already pretty powerful. Acid Splash...well that one just needs to be converted back to the proper 5e format entirely, reducing AC is a huge buff. Ideally, cantrips shouldn't create surface effects at all because anything that just straight up ignores AC, no matter how little damage it causes, is OP. Sure maybe it only causes 2 damage per burn tick reliably, but literally all you have to do then is make a big area of fire between you and the enemy and those tiny little burns will stack up until they die without you ever having to even target the enemy directly.
