Imitating an MP-E using a reversed zoom

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BR recommended two old Nikkor 35-70 lenses for reversed macro use
http://www.naturfotograf.com/lens_zoom_ ... F35-70f3.3
I believe the extension due to the butchered zoom helps improve quality in such applications because the sensor comes closer to the min. focus distance position (the lens should be set to close-focus, in case it has CRC). Also the reversed-electrified-kit projects would benefit from some extension. BR suggests a diopter lens as an alternative to extension.
Some Nikon DX zooms I've tried are useful at the wide end of the zoom but towards longer FLs the quality quickly degrades. I guess this is probably related by the MFD being shorter at the wide end.

Improper placement of the aperture tends to result in vignetting rather than stopping-down, and sometimes also changes perspective or such.
An aperture diaphragm which is closed just enough to let the whole image pass tends to act like a light-baffle, cutting stray light due to oversized light-circle, which may otherwise cause veiling flare/spots/ghosts.