[dotnet00]

I'm fairly certain that the effect of point b is just a version of the pendulum rocket fallacy. There is actually no change in stability of a rocket in flight related to if the engines are on top or on the bottom because the tidal forces exerted by gravity are too negligible in that specific case and otherwise gravity is acting equally on the entire body.

Plus, since the engine is typically one of the heaviest parts , and the lander isn't a two-part design like Apollo, the fuel tanks are mostly empty upon landing, and therefore the center of mass is low due to the engine.