Rethinking my mobile setup

Alright, the shortened UHF-only Nagoya UT-106 is back in service.

I added a piece of RG-58 with PL-259 so that I could measure SWR. But just the fact of terminating the coax with a PL-259 made me think of a way to fit the QYT KT-8900 mobile in the new car in place of a handheld.

While the large glass roof drastically reduces the flat metallic area for a magmount antenna, it does not block RF either. Since the only place for a small magmount is above driver's head, the antenna cable would be in the way of the passenger because I don't leave the antenna outside when the car is unattended, go figure. But there is plenty of space in the back of the car. Yes, inside, but with all those transparencies (be it glass or plastic), RF-wise it is almost like being outside.

The plan is to place the magmount base on a metallic surface and let it rest on the parcel shelf. At home I found an L-shaped 40 cm long iron piece that can be forced between the back seat and the shelf. SWR of this combo is 1.5:1 on the FT-817. So far so good.

Will it work?