The flare factor is calculated by how much the shadow exposure is affected. I believe the standard practice is to use the shadow exposure 4 1/3 stops down from the meter exposure point of a statistically average scene luminance range. A one stop filter factor means flare doubles the shadow exposure 4 1/3 stops below the metered exposure. If the luminance range is shorter than the statistically average and the shadow exposure doesn't reach down 4 1/3 stops, then there's nothing there to add exposure to. Where the shorter luminance range shadow falls in this example will not experience a doubling of exposure.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).
Within the same optical system, the only way to change the flare factor is by a change in the luminance range or change in the portion of dark and light tones in the scene and how they are distributed. Adding or reducing the camera exposure should just move back and forth along the x-axis.
Currently reading about K in Henry's book. If I didn't already understand what the K-factor is, I still wouldn't know after reading that section. Another example of how he just might not be into theory. Still have the testing for K to get through.