As Philip said, these cases work fine, I believe, if you flip the normals of the bottoms of the cylinders with the spread-out bottoms.

Boolean is intended to work with things that represent closed volumes, for the most part. (Maybe a to-be-implemented-in-the-future mode could deal with the oft desired "just trim away" case, which is what is desired here.) Closed volumes should have manifold edges and face normals that point to the outside. Since these models do not conform to that, the fallback code comes into play, and that code too assumes that the normals at least try to indicate which side is "outside". So while the results are not great here, the input is not in the form expected for Boolean, sorry.