Mmmm ........ these are quite different from my hot spot experience.
I have a few lenses that do not like IR, but the hot spot is larger than in these images and does not show signs of the aperture blades despite being taken at f11. So more like the central area having considerably more exposure. This I believe is light bouncing back and forth from the AA filter on the sensor and the lens rear element.
The quality of the lens for visible light photography appears not to be a factor here so there may be something in the lens coating.
My Nikon lenses that hot spot on IR are 12-24 zoom, 24mm f2, and 28mm f2.8.
20mm f3.5 is fine on the 6mp D100 but hotspots on the 12mp D2X, yet the 35mm f2 is brill on both cameras.
Unfortunately I seem to have binned my tests but can re-do if wanted.
Don