I know that posting same post in two threads is a no-no, but this will finally sort out confusion over stepped noses, how can Mclaren avoid not to have it, and other similar questions.
People, have mixed min and max height regulations.
FIA wrote:15.4.4
The maximum height of the survival cell between the lines A-A and B-B is 625mm above the reference plane.
The minimum height of the survival cell between the lines B-B and C-C is 550mm.
So, car can have fully horizontal chassis and nose at 550mm and no stepped nose, or B-B at 625 which is max. but dropping towards front with A-A at 550, and again no stepped nose. That is how Mclaren has done it. Their chassis has continuous declination towards front end, and it continues at same angle further down the nose.