Dave I'm not sure we're saying different things.. as you still say it's technically possible, but not a good idea. agreed.
But if you were transmit on 70cm with a 2m antenna to a truck that's is 50' behind you, I'm not sure he wouldn't hear you. We can try with one of your radios..
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05 525EXC, 01 XT225, 07 TTR90, 07 CRF50