Thank you for your answer.
Despite your help on both of my topics I decided to drop the nDisplay plugin since there is not enough documentation for my use case and the community seems rather small.
But I will try to explain how I got there, maybe this could help ppl in the future.
First I think nDisplay lacks a lot of documentation when it comes to the MPCDI type of projection. The only supported MPCDI format is 1.0 which is not outdated since the standard is 2.0 now.
Also, except a link that directs to the MPCDI website there is absolutely no details on how to use it.
I had to make a lot of guesses based on the documentation of the MPDCI 2.0 format and hope that it still works for 1.0.
after downloading the sources of UE and looking into the MPCDI reader of the plugin I figured out some of the tags of the 2.0 are different from the 1.0 (mostly uppercase difference if I remember correctly)
For the pfm file, there is only documentation in the MPCDI documentation as well, even though there is a way to directly input pfm files in the configuration file of nDisplay.
To my understanding, pfm stores the XYZ position of each pixels and based on the MPCDI documentation, it does not require to be the same resolution as the display since there is an interpolation parameter in case it does not match. The only requirement is that it is at least a 2x2 res file.
Since I was trying to make it work with a multi display system that does not export as MPCDI natively I had to make test data by building myself a custom pfm file creator program which is how I got to a 32x32 points (since it can be interpolated according to the MPCDI doc)
anyway, I spent way too much time trying to make it work, and not finding any useful information anywhere that I decided to try to make my own multi window system directly using Slate inside UE.
I am not trying to trash talk nDisplay but I hope my criticism can give you clues on what needs to be improved.
Mostly the documentation to my opinion.
Thanks for your help anyway.