Here,
there's a recommendation (the two first sets of times, by Anders) for 35mm and 120 HP5+, with very different EIs and development times for both formats...
Can someone please elaborate on the reasons?
Thanks.
It seems to me that those recommendations are for very specific types of negatives, most likely preceded by extensive testing. Even if you take them literally, you are unlikely to obtain the exactly same results. I would suggest following the manufacturer's recommendations, as
@Sirius Glass suggests, and then, doing your own testing to determine what works for you. By the way, even if the same emulsion is used for 135 and 120, there might be subtle differences in how each format responds to exposure and development, which is probably what the author found out.