The more I look at the original picture I wonder if the manufacture expects to have a gap between the box and fixture because of stucco, brick, etc that could be used to allow the wire to enter the box.
I know that the light fixture boxes on my house (built in 1950) are not flush with the finished stucco by maybe 3/16 of an inch. That would allow me to use this fixture and run the wire into the box without pinching the wire depending on how long the mounting screws are.
