I wonder if some more experienced and senior (in the literal sense) amateur
could explain to me one difficulty that I have in understanding single
signal
reception with the crystal phasing control?

AIUI, the phasing control is adjusted so that the frequency that would give
the audio image is phased out by being in the notch.

If that is true, how is it then possible to adjust the BFO to a
pleasant-for-you tone,
because such adjustment will alter the CIO frequency?

Surely the BFO has to be set in advance to be halfway between the serial
resonant
frequency and the notchable parallel resonant frequency?

This is a query stimulated by my current project which is to build a
boatanchor style
RX, with a flywheel-loaded slide rule dial like that of the Eddystone EA12