I notice that upthread Defrost mentioned that according to her Mazda 5 manual (2007 model), the third row headrests must be down before installation and tether routed over the headrest.
Shoot! I never noticed that in my 2009 manual! I'll have to look it up since all the installs I've ever done in the 3rd row have been with the headrests completely removed!!!! Luckily I rarely have seats in my 3rd row since the kids are always in the 2nd row except for when my mom comes to visit.
For some reason I can't edit my OP and I have some more seats to add:
Britax Frontier 85: 2nd row, LBP, no problems (I can't get solid install with SBP like I used to with the original Frontier)
Britax Roundabout 50: 2nd row, rf'ing w/ LATCH, no problems