From what I remember, there are 3 dementors at the end of act 1: one in the center that goes down on top of the orchestra, then flies around the front of dress circle and all the way to the balcony. The other 2 dementors are on both sides of the stage.
For the dementor that goes down the center orchestra, I saw it for 3-4 seconds and then when it goes to dress circle I still see it but when it goes to balcony that's when I don't see it. Even when I sat in front orchestra, I had to turn my head around and look up to see that the dementor was by the balcony.... to me it's meh.
For the scene in part 2 with the neon lights, you can see both the writings on mezz overhang and also on the theater roof from row S. Even during the points when they travel back in time, you can see the entire stage and the top of the arcs do that special effect that made it look like it was bending/moving. Row S is fine.... I'd say row Z or even row W that's when mezz overhang issues may bother people.