Hey!
I found the solution for the issue. It was on my end.
Somehow Arma3 seems to think my resolution must be a triple screen, so it only displays info on the center screen, which makes the overlay a 16:9 format in the center again.
I had to edit my Profile file to fix it. ("C:\Users\XXXX\Documents\Arma 3 - Other Profiles\XXXX")
It is the "tripleHead=1" which I set to "tripleHead=0", now I have the overlay fit the full screen.
sorry for the confusion