SWR with amp on wierd situation...

[Mentor3006]

*DISCLAIMER* this is entirely an academic excersize and should only be considered theoretical, I am not advocating for or saying I have or would violate regulations.

This was hashed over in a previous thread a long time ago, but didn't cover this issue. The old thread was [Please login or register to view this link]

Scenario. Guy living in the boonies, with multiple vehicles, each equipped with idential radios, and amps, but different antennas...

For the sake of discussion the radio rigs are Cobra 148 GTLs with Cobra Power Mics, dead stock, and backed up with RM Italy KL203P amps.

There are 3 vehicles / radio rigs in question.
Vehicle 1 is a boring as sh*t box sedan, let's say for argument sake a Chevy Malibu that has been beaten like a red headed step child... it has a K40 coil antenna on a triple magnet mount smack in the middle of the roof. SWR across the band.
Vehicle 2 is a work truck with a covered utility box and a 102" on a ball mount on the front fender. I know ugly as sin but 1.1 SWR across the band.
Vehicle 3 is the family SUV, with a Wilson 1000 mag mount put right in the middle of the roof of the vehicle, with the base of the antenna about 3" away from the roof rack cross bar. SWR across the band.

Switch the amps on. Vehicle 1 and 2 SWR wiggles a bit up, just under 1.2. Vehicle 3 goes up to at least 1.8, as high as 2.2.

Swap amps between vehicles since they are the same. Same results. Swap radios, same results. Move the Wilson 1000 to vehicle 1, SWR is fine. Not going to do the K40 on the family SUV as that is the wifes car and she is already annoyed at the Wilson 1000...

I am thinking issue could be a grounding issue on the car, or the proximity of the cross bar. Maybe move the antenna position a bit further away?

What is the expert consensus on this hypothetical situation?