The Mobile antenna websites practically tell you to keep the coax at 18 feet, or
else. I thought that was true, until numerous people at this group and several
websites said that is nonsense.

For a NGP antenna, the shield is the counterpoise, and if you change the
length of that, you'll detune the antenna. If you can alter things by
moving the coax around, you've got a problem. Think of coax as a
"signal hose". The RF should stay inside of the coax, not run along
the outside and affect things. If things change, start by fixing your
ground. That's one reason I took my antenna off the magnet. The other
was so that it won't get knocked over by a low branch on the trail.

I immediately noticed the antenna worked better with a real ground.