"shearing the projection matrix" reads to me as "move the camera down
No ZombieWoof, you've missed the idea. Think of the camera as having your monitor surface floating in the 3d world in front of the viewpoint. This virtual surface is in "normal" situation perpendicular to the view direction, and centerd with it (the view direction intersects with the center of the monitor surface). Everything gets projected onto this surface and is then rendered in the viewport. When shearing the view matrix, you make this "virtual monitor surface" not perpendicular to the view direction any more, and/or not centered.Tilting the camera ( = rotating as I understand what you mean) won't change the fact that this surface is perpendicualr to the view direction.