Due to production tolerances, which were wider in the past, a lens is rarely its marked focal length. Some lens are designed with shorter than their marked focal length back focus so that they will work on more cameras.
A 127mm may be optically 123mm to 130mm while a 135mm may be 132mm to 138mm. There may be enough adjustment range of the HM RF that a marked shorter focal length RF will adjust in on a lens that is marked with a longer focal length but optically measures close to the upper limit of the shorter focal length.

I have a 135 Xenar that infinity focuses a good 5 or 6 millimeters closer than my 135 Optar which has a factory cam for 136.4mm and is spot on wide open. I also have a 127mm Ektar so I plan to see if the HM RF on the Anny. Speed will adjust to the Xenar one of these days.