The flat area is the area that is suppose to squish into the flat area on the head.
The dish is cut out of basic flat top on the compression side to reduce compression.
The valves in an FE head are at about 13* and open into the chamber at an angle.
Although I do not have a K Black piston in hand if you look very close you may find
the valve notchs are different sizes. This may or may not be the case with your pistons, but it is standard.
The large notch obviously goes to the intake valve and small...
The notchs in the piston are cut at the corresponding angle to the head.
If any portion of your piston is above the block deck then you have a problem.
These piston types are made to yeld about 9.5 to 10.5 to 1 compression +or-.
I'm no spert, but I know your picture does not look like all the other ones or what I have seen
in the flesh.
I've been standing in front of a mill most of my life and still have to meassure twice or three
times and go back and have another peek at the drawing and then cut once.
It's worth having another look just to make sure.