From other similar tests with Attributes Gain :
Main Level 0 to +63 > +12 db
Track Level 127 to 108 > - 3 db (108 is default)
Track Level 127 to 64 > - 12 db
VOL = +63 > +12db
VOL = -32 > -12db
I’d set MAIN / CUE LEVEL to 0 because it increases SRC3 MAIN / CUE recording Level.