[262]The question is which amp? A 1968 100W Plexi with over 500V on the plates or a 50 watter with around 360V on the plates? The response of those two amps will be completely different at the same quiescent dissipation due to the different plate voltages. The 100W amp will require around 35 mA for 70% dissipation. The 50W amp will require 48 mA. Since the transconductance of a tube is fairly independent of the plate voltage the 50W amp will be operating in a much more linear region. However, it will clip the grids sooner. If you load up, say, a 1959SLP model in the Axe-Fx you'll notice the bias is lower than the 50W versions. This is why. This is also why a lot of people prefer the 50W Plexis.
Then we need to ask what type and brand of power tubes? NOS? The response of the tubes is dependent upon the exponent in the tube equation. The original Childs-Langmuir law says that the exponent is 1.5 but real tubes exhibit an exponent somewhere between 1.2 and 1.5. The greater the exponent the less linear the response.
Finally we need to ask what is the output transformer primary impedance. Is it 4K per pair? Is it 3.6K? Is it 3.2K? Primary impedance was all over the map in those days.
All these things interact. The hotter the bias the more linear the response, the higher the gain, the sooner the grids clip, etc. A good amp designer will balance all these things along with the transformer matching to get the desired response.
The correct answer is turn it up/down until it sounds how you want.