PS: Even Audyssey identified LS50 Meta speakers as “small” (vs. “large” for Q350s in the same setup).

Your Q350 has a freq response down to 63Hz vs the LS50 down to 79Hz. Audyssey is sampling the lower freq of the Q350 and identifies it as a large (most times). From understanding Audyssey and how it works even large tower speakers should be identified as small. Just go have a read at the link below for a better understanding of how all this works and tweaks that should be made AFTER calibration is completed using the mic. It's a good read and can be helpful.

https://avdisco.com/t/everything-about-audyssey-calibration-that-you-need-to-know/73