If I can toss something in...
I've had several BH machines, starting with a Discovery 2000, Discovery 3000, Time Ranger, Land Ranger, Discovery 2200 and 3300. If I'm not mistaken (and someone please correct me) none of the BH/Pioneer/Discovery machines have an adjustable ground balance that works in the discrim mode. Several have adjustable GB but they only work in all metal. Even if you ground balance in all metal, it reverts to preset GB when you switch to discrim mode.
The problem is that if you are detecting an area with tough ground (highly mineralized), these machines will struggle in discrimination mode.
This isn't the machines' fault per se, as most machines with a preset GB will suffer from impaired performance in these settings.
When I took my Time Ranger to areas where the ground was more neutral, it performed excellently.
Now, because of my ground conditions, I only use machines that have user adjustable ground balance in discrim. mode.
My two zinc cents.
w