[Elecraft] Can't calibrate K2 narrow RTTY filters to 2.2KHz (high tones)

[Guido Tedeschi]

As I wrote in my last message, on K2 #4334 I was not able to calibrate the
narrow filters on RTTY normal to center high tones (about 2.2KHz): I reach
about 1.6KHz and then the BFO resets to the intial frequency.
It happened only on RTTY normal (LSB), on RTTY reverse (USB) I was able to
calibrate correctly the filters to match the 2125/2295Hz tones.
During the BFO calibration,  I had to add 68pF and 100pF in parallel with
C174 and C173 to have the correct BFO range (4916.77 KHz - 4912.59 KHz), do
you think that I can't calibrate the filters because the BFO limits are not
yet enough (too high or too low)?
Any suggestion?
Thanks and 73
Ciao
Guido, ik2bcp