CVT Mt Rainier on frontrunner bed bars

I recently got a diamondback with front runner bed bars. I have a CVT Mt. Rainier tent which used to be on CBI bed bars. The original CVT mounting straps were too short to use with the wider front runner bars, so I looked at front runner's website for a mounting solution. It wasn't clear that any of them would work, so I called and explained the circumstances. They told me to get the hardshell mounts for my application.

They arrived today and do not fit the tent rails at all. The width of the plate that slides into the tent rails is fine, but the thickness of the material is 2-3x too much to fit in the channel. I'm going to attempt to return my $300 in brackets (I needed 6 and had to buy 8), but before I just cut aluminum flat stock I wanted to check and see if anyone knew of a mount that worked. TIA
Original and frontrunner bottom straps


Original sliding plate in channel

Frontrunner plate is way too thick


Big difference in thickness, but width was correct