Music Hall MMF-7

Wondering about VTF on my TT. I cant seem to crack the hex key nut under the tonearm to adjust VTF. Seems really delicate and i dont want to strip it. I called Roy Hall at Music Hall and he asked why I wanted to change it,"the VTF is preset at the factory." I said Huh! what about heavier vinyl profiles such as the 200 gram designs? He reiterated it was factory set and made me feel silly for even asking about it. Whats up with that! Anyhow,anyone have any luck adjust this on the MMF-7?