Experts, correct me if I am wrong, but what I have learned (or think I learned) is that a longer antenna MAY get you better reception, but location of the antenna is just as important. I short antenna in the middle if your car (roof) will most likely out perform a long whip mounted on the front corner (depending on your transmitting direction).
With that said, a GENERAL rule of thumb with fiberglass (firesticks, etc) is that you want 2/3 of the antenna above the highest point on your car.
One thing to remember though, no-matter what antenna, where its mounted and how well its tuned, a CB is still essentially line of sight, you will not be able to bounce out of a canyon or over mountains.
If you want range, get a ham license and you can get MUCH greater range. I use my CB for "convoy" communications when in a group that are not HAMs, so antenna doesn’t matter to much, as the range needed is VERY small. I have a ham radio for when I actually need to reach out and touch someone.
Hope this helps, and if I have anything wrong, please correct me experts.