Originally Posted by tFUnK

I get that there is asymmetry in the clearance gaps, but what about if you look at the wheel compared to the seat tube? Does it line up with the seat tube?

Your comment "it follows the cassette", refers to the fact that if you flip the wheel, it's now the drive side (not the cassette side) with the greater clearance? Or did you mean the opposite? If the wider gap is on the crank side after you flipped the wheel, then it's a wheel dish issue. If it's still on the non-drive side after flipping the wheel, then it's the frame.

Fwiw, I seem to have slight asymmetries in nearly all of my frames; this becomes more apparent (as you pointed out) when you push the limits with wider tires. It's almost always asymmetric by a couple to a few mm, in my experience. (If I'm wrong then uh-oh I need to check all my wheels and frames.)