Cliff (Fractal) talked about this when modelling the shiva, his quote belowTo me the Bogner quirk is that they have so much less high end than many other amps that the treble knob is totally useless under about 5-6, and more normal settings are like 7-9. Similarly turning presence up helps.
"Human nature is to put the knobs near noon. We are reticent to deviate much from noon. Amp designers exploit this and use different tapers to change the sound of their amps WITH THE KNOBS AT NOON. A prime example are Bogner amps. Everyone says "Bogner amps are dark". No they aren't. But he uses a Log10A taper for the treble pot. It's a standard Marshall tone stack. Usually a linear taper pot is used for the treble. The treble knob at 5.0 (noon) on a Bogner is equivalent to the treble knob at 1.0 on a Marshall. People put the knob at 5.0 and go "wow, this amp is dark". No it isn't. If you turned the treble up to 8 or 9 it would sound a lot like a Plexi but humans are reticent to turn the knobs to extremes. Amp designers know this and exploit it to give their amps a "signature sound"."