JDB beat me to the observation that one has to be biased wrong by definition, but your measurements seem to suggest they are happier with one back biased?
I looked into a somewhat similar topology (22uf to ground with 360 ohm R in series). This was in a gain stage for a phono preamp (did I say this was a while ago
) . Looking into the large aluminum electrolytic as a HPF I found the ESL and ESR were compelling sources of error. I forget the actual numbers but phase shift at 20 kHz due to the non-ideal characteristics of electrolytic of the day caused tens of degrees of phase shift in my actual circuit. Note: since I was in a preamp front end, my cap was only seeing tens of mVolts of AC swing.
While some will argue that phase shift isn't audible (or THD at -100 for that matter) but screw them.. this is science...
Regarding the old popular wisdom of paralleling electrolytic with small film caps, I found on my bench, at least for phase shift, you are wasting your time unless you parallel with no less than 1/10 of the larger cap's capacitance. So paralleling a 22 uf electrolytic with a 2 uf film is still ridiculously large. While I did find tantalum to deliver superior HF impedance at 20 kHz compared to aluminum of the day, despite their bad rap for dielectric absorption et al.
If you are really serious about opening up this can of worms, there is a lot to look at.
I wonder how the modern low ESR caps do for voltage coefficient and DA... I expect they will be dramatically different than my aluminum bench samples from 30 years ago.
But at the end of the day, the only good cap is no cap... I hear you can make HPF and LPF in the digital domain without having to kill any capacitor trees.