For me, it is easier without the math. By "it" I mean the [Scheimpflug Princple][1] of course.

This is the mental model I use. It explains an untilted lens in terms of tilted lenses rather than vice versa.

1. Apparent depth of field is always wedge shaped.
2. The knife edge of the wedge is where the plane of lens tilt and the plane of the sensor intersect.
3. At infinity focus the axis of the wedge is rotated perpendicularly to the intersection.
4. Aperture determines the thickness of the wedge (along with angle of tilt).
5. This means that the more tilted the lens the closer to the camera the "hinge" where the planes of the sensor and tilted lens intersect.
6. The less the lens is tilted the further away the "hinge" of the wedge is from the camera.
7. In normal circumstances when the lens is untilted, the planes are parallel and the hinge point is infinitely far away and the wedge is constant depth.
8. Less tilt moves the hinge (and base of wedge) further away from the camera
9. More tilt moves the hinge (and base of wedge) closer to the camera.
10. Minimum focus distance tilts the plane of focus the least.
11. Infinity focus tilts the plane of focus perpendicular to the sensor.
12. Beyond infinity focus tilts the plane of focus more than 90 degrees (you probably need a view camera).
13. For a given angle of tilt, the longer the actual focal length of the lens the further away from the camera the "hinge" point is. Large format cameras with their longer lenses provide more control over tilted focal planes. For example at two degrees of tilt, the hinge point is further away for a 300mm lens than for a 50mm lens.

The counter intuitive parts of the model for me:
+ Lens tilt does not correspond to the obliqueness of the subject plane. Any tilt can be used to set the plane of focus *parallel* to the subject plane.
+ Focus distance of the lens only tilts the plane of focus.
+ With typical "35mm" focal lengths, putting the plane of focus on a distant object requires only the slightest of tilt and quickly becomes impractical.
+ The closer the subject the more tilt you need.

Yes it is possible to work out all the math, but it is simpler to understand the basic relationship. 

a. Actual focal length and degree of tilt determine the distance of the hinge point (and therefore from camera to plane of focus).

b. Focus distance determines the amount the focal plane is rotated about the hinge point.

c. Aperture determines the thickness of the depth of field wedge.

d. An untilted lens has the hinge point infinitely far away from the camera and the depth of field wedge is a constant thickness.



  [1]: https://en.wikipedia.org/wiki/Scheimpflug_principle