Update: So there isn't room enough for an optic in the housing but I was able to file down some reflectors I had lying around and stuck those on. They're filed down to about 10 mm. They just happen to fit perfectly over the Luxeon bodies. They are from BestHongKong and are meant for the Prolight brand of LEDs. Because the reflectors have been shortened quite a bit they let light out at broader angles, so off-axis visibility is still quite good while visibility from behind is significantly increased. I think I'll stick with this version. Even on a bright sunny day the light is very visible.
Pics - The Mars 3.0 is on the seatpost for comparison. There are two rear shots: one auto exposed and one less exposed.