That 8X multiplier is my point ,,,per  314.28(A)(3),,,,,,,,,,,,,,,,,#1 smaller dimensions may be  allowed.......if and when........#2 fill is less than  allowed........when marked.......and listed.......with the number of  conductors allowed.
Lets use 4/0 as an example,,,,,,,max fill of a 4" conduit is 11  conductors and lets say we are only going to use 4 and the manufactured  had tested.listed and marked the fitting for 6. Then according to  314.28(A)(3) the overall length can be reduced,now reduced by how much  is not the question and the answer must be the standard manufactured  length of the fitting itself that is listed and marked.
Thats where the disagreement starts,then someone says,"Thats not what  that means" and someone else says you are right,"It means this" which is  different than the 1st etc etc etc
I'm not confused are you or are we all




  so maybe what the OP author saw was an installation based on the above   but where 3,4,5 or 6 conductors was going to be used.The decision to  install in that manner had to be based on something.
I'm not disagreeing on the 6 or 8X notations, starting parameters need  to be established if rules are to be written and then additional rules  can amend,How many times have you heard"You need to be a Philadelphia  Lawyer to read and understand that".
dick