sorry, can’t tell you that for sure!
in my understanding the different settings (channels on your projector) do mask
the image (just like the different masks used for 35mill) and then optically zoom the
picture to fit.
but for the sake of professional delivery i wouldn’t recommend to do it that way.
in the good old film days there were also a lot of “full frame analog copies”, and
when you showed them in the wrong aspect you could see the boom etc. of course
this shouldn’t happen, but it could. it never can when you mask your master yourself.
but then again: also the dcp-authoring-software let you normally decide to do this.