Generally speaking higher is better, there are exceptions and sometimes you need to move the antenna around AND up and down to find that sweet spot.
I don't know anything about that antenna, but just looking at the picture, I think you can do better with a known brand and roof mounted.
Mounting the one you have on the roof and adding an extension to the mast to get it higher won't cost much and might do what you want. A newer, (better), antenna won't cost that much either.
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