Been fiddling with my muff

and i've noticed that high up the fretboard its fine but on an open E etc the bottom end has disappered.
Is this to do with my settings on the muff
Tone 2 o'clock
Sustain 11 o'clock ish
Or is there something i can do on the amp.
Or should i just use my OD pedal for the low and the Muff for the high
Thanks in advance