Chris, as they say a picture is worth a thousand words. I think that's a new JL? My JK, and previous jeeps, didn't have bolts around the cowl. Looking at your pic I have to ask what antenna that is? It looks almost like a low cost antenna with a shock spring, that has been covered with heat shrink?? That may just be the way it looks in the picture, but it makes me wonder about the performance of it, since that was the point of your question. I hate to say this but that could be limiting you. A cheap radio with a great antenna is going to get out better than a great radio with a cheap antenna.
I'm not familiar with that mount, I googled it but couldn't match it up. So I'm not completely sure of the how all the bolts connect to the body ground. Even though it is mounted to factory assembly bolts, I would be sure that you have a good ground. It's not uncommon for those bolts holes to have paint in them that prevents a good ground, same thing with the powder coated mount itself. You could have a good ground on the mount to the body but not the antenna connector going through it. You may have to scape a place off at each bolt, and where the connector goes through the mount, to get your ground. Gotta have bare metal to metal at every connection point to get a good ground. Something else to think about with Ham Radio output, is your RF. You have put yourself closer the the RF with the mount on the drivers side windshield area. Those type mounts are actually designed for CB's since you are required to have one for communications on most of the large organized events. You don't have to worry about that with a 4W CB.
You have to remember that your ground plane radiation pattern will be very limited on the drivers side, and truthfully you best direction for effective radiation will be roughly in the direction of drivers windshield outside edge to passenger side rear corner. Basically looking down from above draw a circle with your antenna at the center and then draw a line through that circle along the drivers side. Without getting complicated anything to the left of that line will not be effective performance. Due to the small size of a Jeep universal they don't always give a good even pattern because of limited antenna mounting locations. The most common mounting locations are at the rear tire carrier for forward/side radiation, or on the exact opposite side of the Jeep from your installation to give front/back/drivers side (Opposite lanes of traffic) radiation patterns. You can sort of make out the antenna mounted to the tire carrier on my old JK, sorry it's the only pic I could find that showed the antenna. the higher the better.
The best mounting location would be top center of the windshield frame but that is not realistic nor feasible. First trip into the woods would knock off the antenna and tear up the windshield frame. (same thing with light bars or anything else mounted to the windshield frame). People that have logged as much time in the woods as I have are quick to tell you that just because it looks cool in the catalog doesn't make it useful. If its mounted on the outside of the body its something to get caught on a tree, or rock. We could talk for hours on those subjects but that's for another time. Maybe at the next breakfast.