Here is some cheap, low-cost advise I have given most folks with similar inquires since 1983:
If you like to use an assortment of coils (like 2 or more), and if you select a wide-range of ground mineral challenged sites to hunt .... get a detector with either automated GB, manual GB, or both.
If you use a detector with a factory preset GB, aka 'Fixed GB', I strongly suggest using a factory stock coil that it might have been calibrated to, or select one single search coil you cold leave mounted for most of your needs or specific tasks. If the chosen search coil appears to have a 'functional' GB setting for your most used Discriminate mode ... go enjoy that detector and coil. That's what I do with my preset Tesoro Silver Sabre µMAX w/6" Concentric coil.
In that case, the SS microMAX has only the one internal trimmer to tweak the Ground Balance. I mounted the 6" coil, then used four mineral specimens and checked the performance in maybe a dozen hunt sites to make sure the GB was not too negative to cause falsing, or too positive which could eliminate the detection of a silver $, a 50¢ piece, or depending upon the particular circuitry and coil mounted, even not detector (hear) a US 25¢ piece or even a 10¢ coin.
As for the Mojave, I wish I had one on hand to open and check to see if there is more than one trimmer. And, unfortunately, I do not know how the circuitry works for the two-position GB select toggle. Just a guess would be that the two GB settings MIGHT have a separate trimmer to adjust the GB for each of the settings, and that would be good ... IF anyone messing with them knew how to Power Balance a Tesoro in the silent-search Disc. mode. Most folks don't.
If there is only one GB trimmer and the two toggle settings are governed in the circuitry, again, someone ought to know how to Power Balance and check each setting to ensure it is functional. In your case, you said the coils you used could work OK, so I would just leave the Mojave as it is, then mount the best coil for most applications and enjoy it.
Monte