Are you sure that the clip you heard was the 2-Knob Bender? While this pedal will clean up some with the guitar volume rolled back, it's not nearly as sensitive to input level as the ESV Fuzz (which, BTW, also has 2 knobs, hence the confusion created when you referred to the pedal as "Fuzz" rather than "Bender"). Also, it retains some fuzz character (at least mine does) even with the volume control on my Strat down around 5. With the ESV Fuzz, it loses almost all the fuzz character by the time the volume is between 8 and 7. The extra transistor stage makes a big difference in this regard.
I suppose I could be wrong. Maybe it was the ESV Fuzz and not the ESV Bender. That would explain a lot. If so, I'm making the entire bias operation harder than it needs to be.
Also, the pedal retains a pretty reasonable balance of volume vs. fuzz/sustain over a wide range of that trimpot's sweep. If we assume that mid-sweep is 12 noon, then anything between about 9 and 3 o'clock still sounds reasonably good--you're just trading off volume for fuzz/sustain. Too far one way and you'll lose almost all of the fuzz, and too far to the other side starts getting splatty and gated sounding. If you just set it in the middle of the sweep, you should be in pretty good shape. Further optimizing can be done by ear.
Thanks for this bit. You are the first to put it in a way I can compare with my own findings. Great stuff!
This is prety much in line with exactly what I'm seeing in my bias attempts. Using your clock model, with 12 noon as the center point, I suppose the pot itself goes from mayb 7 o'clock at minimum to around 5 o'clock at maximum. There does seem to be a lot of "action" between 7 and 9 0'clock - basically going form almost no fuzz (and a pretty bad sound with the guitar volume rolled back) to boom!, fuzz! in that range. Things do remain reasonably constant from 9 to 3 o'clock. At the top end, from 3 to 5 0'clock, it's pretty much as you describe. The fuzz just becomes a bit over the top and sort of useless (makes the pedal's fuzz knob almost a waste of time).
Knowing this, I think I'll focus my efforts on that 9 to 3 o'clock range. From the other day, I do recall that there were some points in there where adjustments at the top range of the guitar's volume (7-10) did affect the fuzz tone. Didn't clean up, but I could reduce some fuzz for a bit of a dirty rhythm tone and then crank for over the to fuzz. I'll focus on that instead of some elusive point where the fuzz is gone (ala a tube amp or even a Fuzz FACE
As Tark has suggested, a couple of photos couldn't hurt. You wouldn't be the first to miss/overlook something that was obvious to a different set of eyes....
If I still think I have problems after trying what I described above, then I'll be sure to post some pics. Heck, I should probably post some anyway. Can't hurt.