[Elecraft] K2 SSB s/n vs CW s/n ?

[PE1E]

When I tune my K2  in a carrier ( all HF bands excl. 160 mtrs ) I notice the
K2 SSB setting has an over 10 dB worse s/n.
I really mean worse s/n, no difference in audio ( gain ).
My calibrated HP 3335A generates the carriers.
My calibrated HP 8568B spectrum analyzer shows the the audio output S/N.

I also varied in numerous combinations the K2's IF and LF gain pots.

I tuned both SSB and CW for maximum signal strength ( not for the same
pitch.).
I guess this does exclude possible non matching filter- and/or  bfo
alignments.

I used the same filterwidths for SSB and CW.
The S-meter shows no difference between SSB en CW ( I varied the carrier all
over S1 until 9+20 ).

What could be on ?

Thanks,
Peter, PE1E