FWIW. I think that Shimano & SIDI are not sized the same ...
While they may be very close to being the same if you wear a size 39 (and apparently, 41), the further you get from that size, the greater the disparity (at least, IMO) ...
My Shimano shoes are 44 (I have a really old SH-R120 pair that are 43.5), and the SIDI shoes that I have are 45 ...
So, depending on your shoe size, you may find the sizing to be different, too.