Guessing the problem was caused by the fact when in top view, the cut project object was 0 wide so using top face of the cylinder could produce much better result than the side faces.
Anyway, the result now I could make looks better, but cannot loop select all the faces at once.
Is there a way to resolve this?
As I couldn’t figure it out I went with the cylinder with the horizontal axis’s cut edge and reconstructed the faces of the vertical cylinder from the right vertexes.