The best location for an antenna is centered on the vehicle and as high as possible, everything else is a compromise.
Most people mount their antennas in locations they like, some locations are noisier than others, so pick and choose.
Tying the rear bumper to the front is not necessary only grounding the antenna mount to the frame/body; making sure the frame/body/engine/battery bonding is good is another thing.
If you intend to mount the antenna on the bumper, get a good ground from the antenna mount to the body and frame, don’t depend on the bolts to do it. Make sure the mount is solid, run some coax and tune the antenna for that location on the vehicle and live with the way it works; it is that easy.
Now whether the old tired and true 102" whip works better than any other antenna, I won't get into it but the newer fiberglass antenna are what is called top loaded, which means they start transmitting at the top, so the chances of getting your transmitted signal out is far better. The magnet mount antennas are usually bottom loaded but mounted high will create the necessary transmitted signal. The loading only electrically simulates the full length of the antenna that is why they are shorter but not short on performance.
A CB antenna is an electrical device; it requires a positive feed from the center connector of the coax and a grounding system. This grounding system needs to not only feed-back to the CB via the outside braid of the coax it has to feed-back through the frame to the battery which creates a ground plane to reflect the signal skyward so someone else can hear which is the negative side of the electrical path. Make sure you have a good ground to the body/frame of the vehicle, using connecting straps so the antenna mount, the body and the frame of the vehicle is all one.
Here I go running away again, sorry for the extra words and if this is confusing please let me know.