Vacuume line fitting at Firewall - faces which way?

[ahoogakev]

Hello A Gang; More trivia; There is a vacuume fitting at the firewall that is seen in this archive picture that Marco and probably others have often posted, I have blown it up and circled the fitting in red.This picture shows the nut facing the motor side, but the JS does not say which way it should face , if any.
I have two examples, on one the nut faces the motor, and on one the nut faces the interior of the car. Both ways work equally well, and this very basic part has almost no reason to ever need removal , at least that I can see.
So my question is, was this fitting installed randomly either direction at the factory, or have others seen it always facing one way? Thanks a lot! Kev.