I have never had to dial in a single MFA number on any of the Canon lenses I have owned (L or non-L), I really don't understand how people have so much bad luck with Canon. Could it be your body that is not calibrated or mine that focuses better (5D3)?
And in owning three different Canon dSLR bodies, I have never found the need to adjust ANY lens (Canon, Tamron, Tokina) for focus accuracy.
Sorry, I didn't mean to just come in and bring in all this negativity. But you have to understand how I have tried SO MANY sigma lenses over the course of years and never got one that actually worked properly.
And in reading so many different testimonies on POTN about needing to buy and return multiple Sigma lenses to find a single one which they are satisfied about focus, and in reading about folks who own multiple Sigmas and send each one in to Sigma warranty repair to get satisfaction with focus for all of their Sigmas,
I remain very leery of buying one myself. When one does not see anywhere near the volume of posts about focus error with other brands, the track record seems to speak volumes, doesn't it?!