Deffo agree with you Garth, some vehicles can be a nightmare to get a decent swr on as can some locations on an otherwise good vehicle with the whip centrally mounted,will also change radiation pattern too,usually in favour of the direction/s of most metal.
Bare in mind the figures i gave for 10m were for a steel whip, I'd expect a 102" fibreglass cb whip would need trimming for 10m too so would be shorter than the 102.26" i quoted for 28.000 Mhz on a steel whip, thats just to resonate it, no guarantee swr will be much under 1.5:1 at band centre and could be higher as you say depending on placement and vehicle.
I'm sure even the ground under the vehicle or surrounding objects can also affect impedance and radiation angle too. A high sided vehicle like a bus or truck drawing up beside you can detune antenna,i witnessed it many times out mobile, it even caused the tx on my old TS50 to trip one day, as I'd been lazy and just fired the hp4000 on, swr wasn't too bad on band E, high end of 27 mhz but i was on band B at the low end of 26 mhz my hunting ground and it wasn't great,about 2.5:1, a lorry came up from behind us under a railway bridge as i was talking to a station in the Bronx,swr went passed 3.0:1 and TS50 is touchy as fuck about 3.0:1.Took a while for it to come back on,but shit happens, just another lost contact. Cracking wee radio mind, don't know why they discontinued that one. Had 2 of them and love them, my first choice hf set,followed by 706,ts430 and my dream machine the ts950sdx,
