Have you ever run into this question and if so do you know where one can find the answer:
Can a mirror be used to reflect a gaze effect such as an antimagic cone that is dependent upon the creature’s gaze in an area? Only if the specific gaze says it can (e.g. a Medusa’s gaze can be reflected back at them).
A beholder’s anti magic cone emanates from the beholder’s eye, but has nothing to do with whether you can see the eye or not.
— Dan Dillon (@Dan_Dillon_1) August 5, 2020