it was shortly discussed here Upload via various Apps make different results - #7 by xsys
And from my further testing, I tested multiple settings and found the final number of MB and segments used is the same for part size 64 MB and any higher. Maybe things have changed since then either on Synology side or Storj side.
Btw. I have set it like this
but in the bucket I can see all files are reported 52 MB size, so who know how Synology is calculating megabytes:
