I put mine on the roof rack but although can hear others ok they cannot hear me more than a few yards away. Have fuel can, tyre etc on roof rack also. Understand could be the aluminium and the very hot weather that causes the problem.
If the bull bar is bolted to to the chassis it should be fine, I ran a cable from the antenna to the battery, cause earthing points on the roof rack and chassis were terrible. Check the earth with a multi meter...
you've not got much of a ground plane with it mounted there
No but I had it in the middle of my roof on my previous 110 and it was only a little better.
I know I'm a bit thick but does a magnetic mount actually stay on a bumper even in severe off tarmac driving say as in Morocco.