Question Secure FFing install in center seat ('03 Subaru Forester)

I'm just a few weeks away from welcoming baby #2 and I've decided that today is the day I'm going to flip DD to FFing. We made it to 3.5 and 39 lbs. I'm pretty happy with that but ... *sniff sniff* Last year, I bought 2 Radians (an RXT and a R100) as they were the only 2 seats I could find that would fit side-by-side in my wretched Forester (this car is the bane of my car seat existence). I checked the install at a store before buying and I was quite happy with the install with the RXT RFing behind the passenger seat and the R100 FFing in the center. We HAVE to have the RFing seat behind the passenger seat. Either other position makes it so that the driver's seat can't recline enough for DH to drive and its our only vehicle. We were really hoping to put DD FFing in the center so that she wouldn't be squished behind his seat (also limiting kicks to the head) and so that we'd have the seat behind the driver's seat open.

Well ... I went to install the R100 by its lonesome in the center and despite all my super human strength CANNOT get it tight enough using the seat belt and the top tether. The base wiggles a good 4-5 inches side to side and the top wiggles a tad less. Not happy. The center seat is humped so I'm guessing that's my issue. I've moved it to sit behind the driver's seat and I get a much more satisfying install there. This will function but its really not ideal. Is there anything I can do to improve the install in the center? I shouldn't be relying on the presence of the RXT to achieve a good install, correct? In other words, both seats should independently have a good install, right? Would it be Kosher to use something like a towel to even out the hump?

Hi. You're right that the installation of each seat should be independently tight. The hump can cause a problem, but there's nothing you can do to try to fix it. One thing you can try on the Radian itself is to put the ff recline foot down. Have you tried that? It's such a small thing and you think it couldn't possibly make a difference, but it often does.