The point incontrovertibly proven with sine waves is that you perceive as having roughly the same volume two signals that are at the same LUFS level, not two signal at the same true peak dBFS level.
Wtf does this have to do with a null test?
Continue with that experiment by perfoming a null test between C and A (or B) and do a LUFS measurement on the difference file: it will show exactly the difference between C and A (or B), i.e the LUFS of what's left under 100 Hz (or over 100 Hz).
Jesus F. Christ!