I have a 4’ NGP antenna on the front driver bumper of the Frontier and a 3’ NGP on the roof rack of the Xterra. I went with NGP because there is no need to be in the middle of a metal panel to obtain counterpose. And there is no need to ground the antenna mount.
On a ground plane antenna setup, you are tuning the cable, antenna and ground plane. For NGP you are tuning the cable and antenna only. The benefit I saw to the NGP kit is, I could move the antenna location without needing to retune.
If I remember correctly, it is possible to gain better performance from a GP setup, if the conditions are ideal. With less than ideal conditions, NGP will have better performance. Center of the hood or center of the roof would be ideal. You would end up with the best ground plane. I’d think running an antenna on the corner of the vehicle would be less than ideal. Since there isn’t really a good ground plane. Especially if it’s a bumper mount. Because most of a 4’ antenna would be below the roof line.
Firestik’s faq site is amazing. I can’t tell you how many times I read and reread the info on their site before I bought. Their info applies to any antenna brand.
Tons of good info here. Click the technical library link in the last paragraph of the home page.
http://www.firestik.com/CatalogFrame.htm