The expanders I've seen do not contact the cylinder wall and are basically symmetrical with no discernible top or bottom except for the ends. I don't see how installing them up vs down would make a difference.
That being said, I've never seen the direction of installation spelled out in any instructions. If it had been, I would follow the manufactures directions.
You're right, they're absolutely symmetrical, except for where the ends come together- They form an arrow of sorts. I'm wondering if when traveling in one direction the expander ring functions better / as intended when that arrow shape may begin to separate and form a gap, pushing out. In the opposite direction the end gap closes. That's the only thing I can think of.
