If I was doing it that way (which would be fine in my opinion) I’d want to do the same for other attacks like the fighter swinging a flametongue sword at whichever layer it is that needs fire damage. I just suggested the attack roll version because it brings it into line with other approaches
In this case, it’s a fucking wall. Just ignore the saving throw and roll for damage. It’s not going to dodge your attack or anything like that.
For blind firing, yeah. You need to do something else. Maybe roll to see if/what they hit, then the target makes the saving throw if it makes sense.
If I was doing it that way (which would be fine in my opinion) I’d want to do the same for other attacks like the fighter swinging a flametongue sword at whichever layer it is that needs fire damage. I just suggested the attack roll version because it brings it into line with other approaches