Robocopy /IPG faster than expected....

[weird_dave]

I wanted to transfer a few files over a vpn which is shared, so I figured I'd use robocopy to limit the bandwidth used, I figured an IPG of 10,000 would at best allow 1 packet of 64KBytes every 10 seconds:

E:\I>robocopy e:\I n:\Library /IPG:10000

-------------------------------------------------------------------------------
   ROBOCOPY     ::     Robust File Copy for Windows
-------------------------------------------------------------------------------

  Started : 15 July 2020 14:20:19
   Source : e:\I\
     Dest : n:\Library\

    Files : *.*

  Options : *.* /DCOPY:DA /COPY:DAT /IPG:10000 /R:1000000 /W:30

------------------------------------------------------------------------------
___ File info Cut ___
------------------------------------------------------------------------------

               Total    Copied   Skipped  Mismatch    FAILED    Extras
    Dirs :         1         0         1         0         0        75
   Files :         8         8         0         0         0         2
   Bytes :   9.640 g   9.640 g         0         0         0    77.9 k
   Times :  43:46:14  43:46:12                       0:00:00   0:00:01


   Speed :               65689 Bytes/sec.
   Speed :               3.758 MegaBytes/min.
   Ended : 17 July 2020 10:06:33

This did not have the desired effect at all, it was more than 10x the expected speed! Kinda glad in a way as 2 days is long enough, but I'd like to understand why it was so much faster.
Anyone experienced this or have thoughts on how it may have happened?