Well I ran some pink noise tests thru my Q-tron since it's the closest thing I have to a Mutron at the moment. Your original guesses were spot on. The low end of the sweep has the resonant peak resting at 185Hz minimum, and the top end rests at 1.9kHz maximum. If you switch the "range" knob to "HI", then those two frequencies become 500Hz and 5kHz respectively.
The LP, BP, and HP positions do NOT alter these resonant frequencies nor the Q of the peak, but instead they do exactly what the names would imply.
LP is a Low-Pass filter. It has a moving resonant peak at whatever frequency in the range the signal voltage tells it to, and it "passes" all lows below that resonant peak. Even when the "bwomp" is up high, the low frequencies are intact. This is obviously the fattest setting. It's also dark sounding because it filters out all the highs above the resonant frequency.
BP is a Band-Pass filter. It also has the same voltage dependent resonant frequency (within the range) but filters out everything below and above that frequency, only passing the "band". This one is thin because the lows are removed. It's also darker since the highs are cut too.
HP is a Hi-Pass filter. Same resonance and frequency characteristics as before, but filters out all the audio below that resonant frequency and only passes the highs above it. This is the thinnest and brightest setting.
I think most of us going for the Jerry Mu-Tron sound use the LP and Lo Range settings. I can tell that in the '70s when Jerry was exploring the pedal, he seemed to also use the BP mode at times, and definitely got weird with the downward option. But once he really settled into the Mutron, it seems that he had settings of:
Upward drive
Gain - to taste and for the right pick dynamic response
Medium peak setting
Lo Range
LP
Brad
... and it's just like any other day that's ever been...
