[Elecraft] K2: A question about band-pass filter adjustment using Spectrogram?

[dw]

Hi all,
I never used Spectrogram for setting my K2 band-pass filters until a
month ago.
I used to set the pass-bands by using the S-meter with a fixed frequency
signal source.

I followed these steps:
1) Zero beat to get a maxed S-meter reading.
2) Dial frequency down until the S-meter drops one LED,  and record the
count.
3) Dial frequency up until the S-meter drops one LED, and record the
count.
4) Adjust the pass-band so that the count is equal in both directions.

I ran the K2 this way for about 3 years, and this month I thought I
would try resetting the pass-bands with Spectrogram.  I’m pretty sure I
was super careful to follow the directions.
But now I’m not sure If I should re-do them again using my old method
because the up/down count is no longer equal.

For example:
With zero beat @ 704031mhz, I adjust RF gain for an S-meter reading of
7.
When I adjust the frequency dial up to 704046 (15 counts) , the S-meter
will drop 1 LED.
When I adjust the frequency dial down to 704006 (25 counts), the S-meter
will drop 1 LED.

Is my assumption that the up/down count should be equal wrong?
Perhaps the pass-band characteristics are such that best setting is not
in the center?
Am I missing something?
Thanks
N1BBR
-- 
 Bw_dw at fastmail.net