stopping down hurts?

[DAdeGroot]

in many cases this may be 'correct' but from what I've noticed, diffraction is more about lens design(design brief??) and less about the size of the sensor.

Partially. Go back and look at the technical link you posted.

Where diffraction is occurring if the film plane is closer to the aperture plane you'll end up with less noticeable diffraction (but it's still there). If you move the film plane further away from the aperture, the light spreads more and thus you get more diffraction effect.

[Tannin]

Where diffraction is occurring if the film plane is closer to the aperture plane you'll end up with less noticeable diffraction (but it's still there). If you move the film plane further away from the aperture, the light spreads more and thus you get more diffraction effect.

Yes, but if you move the film plane you are altering the focal length. In fact, for every doubling of the distance between the film plane and the aperture stop, we have an increase in the f number of one stop unless we also alter the size of the physical aperture stop. (Technically, focal length is measured from the the rear nodal plane, but that detail need not bother us in this context.)

In other words, DA, if you move the film plane, you are by definition changing the aperture.

The moral of the story is: forget all the complicated stuff, the sums all cancel out - diffraction depends on your f/stop. Nothing else.