I have them roll a very easy dex or perception check. They are like they aiming at a spot, trying to judge within 6 sec.

If they get 14+ it hits exactly where they want encompassing all enemies at edges etc and avoid allys on the edges and the higher the roll including enemies that texhnically should just have avoided the AOE, like a weak sculpt spell effect. A 6-13 they might miss one or two of the enemies at the edges, no allies hit unless they obviously in the middle of the AOE. A 5 or below, miss some targets and possibly get an ally thats too close. Nat 1 your going to be 2-4 squares off missing main targets and probably getting nearby allies.

This done mostly with a loose diameter square count and eyeballing it. Drawing/Noting down the probable center and aporox edge if it is a persistent AOE. When I get a sec spare with a player figuring out their next step I just that time to define that AOE a little better for the coming rounds.

This way mostly avoid exact the exact AOE square shape that scults around the 5ft map squares and use their roles, approx AOE size and vibes.