Typically, if you specify tray 4 it will print to tray 4 only.
If you print to Letter LEF paper and don't choose a tray it will choose the first try that has that, run it empty, then switch to the next tray that has exactly the same paper programmed.
If an Application makes the choice (Like MS Word) it doesn't matter what the driver or printer wants.
So in Word, note there are to Auto selections, the 2nd one (not blue) typically works, where the first one does not. It seems in my experience that what Default tray (Automatically Select) actually means is "Automatically choose whatever the printers default tray is"
For fun, that is the default selected option in MS Office.
In Acrobat/Reader, there is the Choose paper source by pdf page size option, if checked it makes all decisions on the size above the thumbnail, so if it shows as 8.5*11.01 it will fault the job because it is impossible to load that stock. No matter what you set in the driver, that checkbox can and will over-ride it.
