Thank for the post Mark.
Yes, what you’ve discovered is expected for the Quaverato. This happens because the high frequency signals have much less impedance going through the pedal input and U2A (the first opamp stage) than the low frequencies. You should be able to adjust the HPF and LFP trim pots (while testing it inline with a buffer pedal) to make it sound more natural. If you want to go deeper, a mod you can do to reduce this effect a buffer has on the brightness of the pedal is to add a capacitor in parallel to R3, which will allow the high frequencies to pass around U2A without being amplified/buffered.
That may be more information that you wanted to hear, but hopefully that answers your question.
Take care.
-Brach