Sometimes in life convention does not apply. I worked for 11 years as a mechanical design engineer (Lift industry) we worked with hydraulics and pneumatics, did a HNC/HND including most of the dynamics, so I have a grounding I can add to 40+ years playing with toys. Lets say its a good practice to mount them vertically, I would not avoid an installation that ended up with that orientation, but I've proved to myself its not a critical element for reliable operation.