Yeah it is a bit to get ones head around but it’s just math and the only thing that matters is if it’s done using real world measurements.
Google is your friend
Type in 100 millimeters =
What comes back is 1 meter.
The easy math comes in as it’s just 10 based math.
2200mm then becomes 2.2 meters as to the size you would expect the height of the door to be.
This puts you in the butter zone because we just verified in fact the the relative scale of all objects in the scene was done to real world scale/measurement.
What are your options. 3Ds Max does not have a built in means of rescaling if you change the SUS while the file is loaded but what you can do if you want or need a working copy of the scene as to source control.
Set your SUS to 1 unit = 1 centimeter and load the file.
When asked select convert to current system units and everything will be scaled to centimeters.
When exporting set the FBX to export as centimeters.
Since it is a real world measurement try (as I’ve yet to do it myself) setting the FBX units to export meters.
The bottom line here though to get you head around it is was the source created using real world scale and if it does then your in the butter zone and you should only have to tell the FBX exporter what was used in the SUS to just keep the right scale.