This extensive comparison incorporates MTF and relates it to a planar subject. And why the 35/1.4 Summilux is a disappointment for any geometrically planar image, which includes a distant landscape.
An aperture series in whole stops or half stops is provided at retina-grade size for the entire frame as well as the generously sized crops. Analysis of both the focus shift and field curvature is related to offsets as suggested by the MTF chart.
While this discussion uses the 35/1.4 Summilux, many fast Leica wide angle lenses exhibit similar behavior and thus it should prove instructive in establishing the best working technique for a variety of lenses.