Distance is, of course, a factor in determining exposure, however there is no such thing as a compensation factor for pinholes, since there is no focus at all, let alone infinity focus, 10M, 3M, etc. There would be no reason at all to apply it in the classical sense. The inverse square law always applies, however. What you do is figure a rough f stop by considering the length from pinhole to film and the diameter of the pinhole. If you change length by moving the standards closer or farther from each other, it will be more simple math to recalculate a new f stop than it will be to use the inverse square law as applied in the formula for bellows extension factor.