The tilt is much harder to show in a diagram because it affect depth of field. Depth of field and the associated out of focus areas are determined by the distance between the camera and the subject for a given aperture setting. Because with a normal lens, the front element is parallel to the sensor plane, the focus plane is parallel to the sensor and the corresponding softness in front of and behind the focus plane.
When we tilt the front element of the lens, the focus plane is no longer perpendicular to the camera sensor, but rather at the angle of the camera's front element, so the the in and out of focus areas are dependent on the aperture and the tilt angle.
Sean explains things here:
https://www.cambridgeincolour.com/tu...ft-lenses2.htm