i've played a lot of ffxiv, where aoe markers "snapshot" when the boss cast bar finishes (meaning that even if you step back in while the boss is doing the animation, you don't get hit; conversely, if you step out after the cast bar finishes, you do get hit)
i've also been playing soulstone survivors recently, which has aoe markers but still use "physical" hit detection (i.e., the markers are purely advisory, the only thing that matters is whether the attack collides with you), and it always throws me off