Take a 90 mm for 4x5 and a 28 mm for 35 mm. For both lenses, light appears to emerge from the back of the aperture and travel to the film plane. The apparent position of the aperture as seen through the rear glass of the lens defines what optics engineers call the 'exit pupil', and it is the size and placement of the exit pupil which determines most of the relevant angles.

Roughly, a 90 mm lens for 4x5 will have its exit pupil 90 mm from the ground glass when focussed on infinity. Stopped well down, light coming from the small aperture meets the corners at an angle of 42° or so.

A 28 mm lens for a 35 mm SLR has an aperture which appears to be, let's say, 50 mm from the film plane. The angle to the corners is now around 24°.

Most ground glass scatters more light through small angles than through large ones. The smaller angle by which the light needs to be diverted in the case of 35 mm is the major reason why you don't see hot spots with those systems.

There is a further factor. Assuming that you are not using a loupe, your eye can only focus down to some minimum distance. In young adults without long or short sighted vision this is typically 20-30 cm. Long-standing convention says a 'standard observer' can focus down to 25 cm. You can do the math for this one, but it is clear that an eye 25 cm from a 24x36 mm patch of ground glass is going to collect light from a smaller range of angles than one 25 cm from a 4x5" piece. The brightness of the 35 mm ground glass will vary as you move your head off axis, but the eveness across the ground glass will always be better than in the case of 4x5.

FWIW, long lenses on 4x5 don't have any hot spot. It's one reason I like using them so much :-)