I believe you can trim the bottom, maybe 1/8 inch at a time but what you will gain will hardly m noticed. I am using one right now, never have touched the dimensions . there are set screws on the coil, in the center, so you can trim either ,from one the bottom section near the coil or the base. then check what your modifications on vhf, have done to the uhf readings. bottom stinger is uhf and the top stinger is vhf. Your swr will depend on the antenna placement. Cener of the roof will be different than a trunk lid mount on the corners of the trunk lid. So before you cut, move the antenna around if your mount allows you too.