Am I correct that, when one extends exposure time due to bellows extension and then extends exposure time again due to film reciprocity failure, the recommended reduction of development time is intended to offset increased contrast arising from reciprocity failure (and not from bellows extension). I ask because this morning I extended an exposure to 2 minutes due to bellows extension, but did not compensate for reciprocity failure (as I was using Acros film). I would like to confirm that I don't need to reduce development time in this case, as I believe that bellows extension alone should not increase contrast.

Also, what are the general guidelines for how much to reduce development time to compensate for reciprocity failure?

Many thanks for your help,