It depends on the helmet and the sunglasses shape. On my current helmet with the glasses I usually wear while riding, going under smashes the arms of the glasses painfully against my temple and/or pulls the nosepiece too hard into my face, so I go over (when I think about it - or ride outside at all, mainly Zwift these days and not at all after being hit by a car a month ago as my bike and back are not functional). Other helmets that aren't as tight against the temple or glasses that don't go as far out before coming back in, and I might go under.