We are the Lone Star Voyagers a chapter of the American Voyager Association. This open forum is for the members and guest of the LSV-AVA. Please feel free to use this service. Remember this is a family riding chapter.
I'm not sure how the antenna is loaded, but if it is too short, you may be able to put a washer or two under the nut where the antenna screws into the base. Make sure they are stainless.
It doesn't matter how many times you cut it, it will stil be too short.
When I mess with setting SWR,using a Firestick-type antenna, in the fine tuning part, I can easily move the ratio back & forth by uncoiling the wire or re-coiling it. So sensitive and adjustable in fact, that I have to anticipate the final reading before I put the rubber cover over the tip 'cause that act also affects fine tuning. I also believe that you can re-lengthen the antenna by splicing the surgically-removed 6" of wire back onto the antenna. Of course, my business is not enhanced by selling you another antenna mast.