It depends on if you are using a anamorphic lens or not.
Projectors are like your TV at home. They are 16:9 aspect ratio. You aren't changing the width of your TV hanging on your wall.
With a projector WITH a anamorphic lens, you actually can change the 16:9 projector into a 2.35 projector by stretching the square pixels into rectangles. Widening the image by 33%.
But, content is designed to use a 16:9 screen these days. Even 2.35 content is designed to use a 16:9 screen. This is why when you watch any movie, even with black bars above/below the image, they look proper on your TV. The black bars above/below the image are actually a part of the video. So, using an anamorphic lens, the image must be stretched vertically (by 33%) before is is expanded horizontally by the lens (33%) to fill the 2.35 space and not look skewed.
Now, keeping everything the same two results occur:
1. You have the top/bottom of the 16:9 image that is cut off because you just expanded it vertically be 33% and threw that image portion away.
2. The image is not expanded vertically, but it is stretched horizontally, which means everyone and everything is fat.
There are two solutions:
1. Remove the anamorphic lens and stop the vertical expansion, and the image appears perfectly on center of the 2.35 screen.
2. Get a projector that can horizontally shrink the 16:9 image by 33%, effectively squeezing it, and then the anamorphic lens will fatten everything back up and make it all 16:9 again. Making it appear in the center of the screen.
It is much better for the 16:9 image not to use all that stretching and compressing, etc. but to leave the image unaffected by merely removing the lens from the pathway.
This is also why I think that people should not use 2.35 screens typically as you are impacting the image quality overall by enlarging it and shrinking it to fit some advertised desire instead of actual cinematic need.
But, that list bit is my own preference, and anyone can do what they want in their setup.