Hi.
You are both incoorect about guitar volume setting (white LED ring of volume knob).
Guitar volume setting has high influence to the patche's sound, especially how you "cut thru" the band mix. And it is ALLWAYS effective, not only with backingtrack playback.
You can easily test it (without any backingtrack playback) by turning volume knob's guitar volume setting (white LEDs) all way down to zero so you do not hear your guitar at all. Then you can gradually increase volume setting and see how it effects.
I have found that setting at about 9 o'clock makes patche's sound "muffled" and it losts especially mid frequencies so it is hard to get thru of band mix.
Setting at about 12 o'clock and higher makes sound much more crispier and more nuanced.
Volume knob's Master (red LED ring) and Guitar level (white LED ring) settings are global, i.e. they influence to all patches, when the Patch level (pink LED ring) is individual for single patch and it's stored with patch settings (this is used for balancing volume between patches).
Regards, Pekka