I believe that is the same picture my Mercedes certified shop showed me when he installed the plugs.
Moral of the story, oem parts by branded names, does not always mean "oem" , because for whatever reason, NGK which probably made the same plugs specifically for Mercedes to install in their cars, have a different grooving spec (although the spark gap is all good). I guess GDI engines can be more "precise" or finicky.
Many combustion chamber designs and spark plugs themselves benefit from where the ground tag is placed ... cooling of the tag when placed closer to the intake valves (avoids wear and premature ignition) ... flame front propagation control ... gosh we could go on forever
Need a camera in there man — thats it the new amg chamber observation option!