According to Douglas Self there is "optimal bias" where distortions are the lowest (he shows charts). Increasing bias above it (overbias) increases distortions. It is trading of crossover distortion with "gm doubling" distortions. Transconductance (gm = voltage to current gain) suddenly changes when two output transistors conduct (class A) instead of one (class B). Perhaps transconductance change is slightly more audible when level is a little higher.
Also, anything can be fixed with deep negative feedback. It lowers THD, IMD, lowers output impedance and widens bandwidth. Deep NFB also produces TIM (Transient Intermodulation) distortions - an overshoot in time domain, that produces higher order odd harmonics making sound bright and unpleasant.
Class AB amplifier has voltage gain of few thousand without feedback while class A amplifier has gain of few hundred. Increasing bias with amp that already has higher gain won't help much - NFB damage (TIM) is already done - it would have to be designed with shallower NFB - but this can make gm doubling distortions more audible.
Class A into Class AB
I’m still a little confused about power amplifiers and integrated amplifiers that are class A & class A/B. Like when they say the first 8 watts are class A then it goes into 400watts class A/B. But the same amplifier can be biased to put out 12watts class A then go into 250watts class A/B. It can be biased again for 18watts class A and 150watts class A/B. etc. Ive read that these amplifiers, ones that can be biased like that...and in general all the "first X amount of watts are class A before going into class A/B"...that those first X amount of class A watts is NOT true class A. If that’s true...what is it then? What’s "kind of" class A mean? What’s the point of a "first X amount of watts are class A" then?