As far as I know Roundabout policy is rear mezz for rush tickets, except perhaps on occasion when I lead it out and they have lots of returns... I know they had better rush seats when Kristin was sick during OTTC. However, when she was scheduled out before the Tonys and I went to see Mamie we still got rear mezz for rush. The theater was quite full that day, it being Tony weekend and her absence being known in advance, idk...
Anyway, rush is *almost always* rear mezz, let's just sum it up as that.
Btw, I sat front row mezz with Hiptix Gold and that was wonderful, so much leg room haha. And it's a very far overhang, the fronz mezz overhangs about the 8th row, so you'll be pretty close anywhere in the mezzanine, even the back.