DPAF in the 70D has two photosites for each pixel. I'm really surprised that no one has suggested that "fine detail" is a selectable mode that reads each photosite separately to produce a 40mp image.
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Are you just burst-shooting and hope for the best ?
It wouldn't affect curvature of field, but it sounds like a way to correct for focus shift (the 50 1.2 L has been known to have focus shift at close distances)