Installing the seat upright will make a big difference, but you definitely can't do it with a Radian. I can install my a Marathon in my tiny Subaru and have enough room sit in front of it on the passenger side, but dh can't comfortably drive in front of it if we have it on the drivers side. In a Honda Pilot, though, it should be no issue.
Of the seats you listed, the Roundabout would give you the most room, but you could do it with the FP Safe Voyage. Basically, when you install it RF, you need to lean on the front of the carseat (by the harness adjuster strap) while you are tightening the seat belt or LATCH straps. That will make it more upright than 45 degrees.
dd1 watching over her brothers and sister from Heaven
ds1 my adorable 8 year old
dd2 my sweet 5 year old
ds2 safely arrived 12/12/11 at 36 weeks
Placenta Increta/c-hyst survivor