I kicked off a fairly large print with PA CF as the base material and ABS as the support filament. The support settings are ABS for support interface. Why does the print calibrate the support filament instead of PA CF?
I guess the support filament is loaded and printed first and afterward your regular material. For Multimaterial - and I consider a different support filament already that way - I see the weakness of only calibration of a single material in memory. Hope Bambu will improve on that front soon that the calibration values can be either displayed/extracted and build into the filament settings, or they come up with a solution that for mm-prints they calibration for all used material.
Don’t ask difficult questions 
Yes the whole calibration thing falls apart when you mix materials in your print.
I suspect you could first add a small object in print material and select print by object to coax it into calibrating the print material.