So do the general Ford/Getrag instructions specifically say 1" or 20mm below? As you're right, 20mm is only ~0.79", so even MORE fluid may actually be needed IF indeed that is the instruction spec to use, which would be likely the full 2.2L as some are saying... but either way, 2L, not qt., should be the absolute minimum to feel fully safe, IMHO. It also appears there is quite a range on shift feel from new between any given FiST. For example, the one I test drove felt great, but then I had the dealer bring in the exact color/spec'd one I wanted, finished the paperwork/bought it before it even arrived/had a free loaner until it did. But when it did arrive, I noticed shifting was not as crisp at all compared to the one I test drove. But it also does not have the obvious "clunk" that the TSB on the half shafts to get repaired under warranty. So perhaps if assembled 100% ideally, then the factory 1.67L may indeed be enough, but if something isn't 100% perfect, then it appears using 2-2.2L is a great alternative to helping with the issue when it's not bad enough to warranty. Maybe that's why that directive being issued from Ford to fill more when repaired or replace to perhaps help prevent further issues isn't a very transparent/vocalized/official thing; they don't want to have to admit that many have issues enough to *maybe* warranty but also know that the additional fluid does indeed help prevent issues from returning down the line.
The bottom-line is if the fill procedure says to fill to a certain level, any listed amount that's less than that should be ignored, the fill level itself is what matters, regardless if that doesn't match what the manual says.
2016 Ford Fiesta Power Train Service Bulletin 458133
Action Number: 10078987
Service Bulletin Number: 458133 Report Date: May 10, 2016
Component: Power Train
Summary: Clunk noise shifting from 1st to 2nd gear
SSM 47327
https://ford.oemdtc.com/1725/clunk-...t-to-2nd-gear-2016-2017-ford-fiesta#more-1725 - This shows it was expanded to '17-'18 as well, but we don't know all the procedures involved, other than just replacing the half shafts, without a subscription to access the procedure manual.