Ok, in the flare example the more I think about what Stephen said I think we can at least remove reflection off the emulsion. So we've removed that element, and removed the diaphragm as a variable by using and ND filter. So the possibility we're left with is simple camera flare. Here is where I'm still unsure - because assuming I don't mask the lens to an image rectangle with projection limited to the emulsion area, the image circle is larger than the film, so indeed additional extraneous light could bounce off surfaces in the mirror box, onto the film and cause increased exposure. Is this reasoning correct?

If that is correct, the question again would be, given the equivalent image forming units of light in the two exposures (1/60 @ f/2, 1s @ f22), would there be a difference in film density for this relatively low density (actual density or "Zone" not really critical, as long as the net density above FB+f is quite low - say somewhere around 0.1-0.2 above FB+f).