@Ma
‘Fader’ refers to ‘THE’ Fader (of pre/post fader fame), which is generally the only fader on an analogue desk.
So this is not the physical fader of a channel strip, which can be used to control any send level, but the internal fader ‘proper’, which refers only to the send to Main LR.
As in the reference guide (https://www.allen-heath.com/media/SQ_ReferenceGuide_V1_5_0.pdf#page=89&zoom=auto,-361,451), you can gang assignments and send levels to mixes using the ‘Routing’ option.
Admittedly slightly confusing, but hopefully this helps.
Thanks,
Keith.