[Elecraft] K3 RF gain cal questions

[Chuck Guenther]

I have performed the RF gain calibration  (and also re-calibrated
the s-meter) on my K3 using the Elecraft XG-2 generator hooked
up to the receive antenna input of the KXV3 module.  I used this input
for two reasons:  One reason is there is no chance of RF coming out
of this input.  Secondly, I have a KD9SV receive antenna switch box
("Dxpedition" model, with preamps for 80/160m) which allows me to
have the XG-2 conveniently available at all times, simply by leaving it
hooked up to one of the receive antenna jacks.  Of course, I left the
KD9SV preamps "off" for these procedures.

First question:
Is there any problem using the Rx input jack for the
RF gain cal, instead of the ANT1 input as directed by the latest
version of the K3 utility ?

Second question: 
Suppose that  I do an RF gain cal, then change the filter
gain (in the Crystal filter configuration part of the K3 utility) of the
roofing filter I used during the gain cal?  Should I repeat the RF gain cal?

Third question: 
What exactly is "calibrated" during an RF gain cal?
I understand in a general sense that the overall RF/IF system gain is
determined by many things, including scaling constants in the DSP.

Thanks & 73,

Chuck Guenther  NI0C
K3 s/n 1061