As long as the signal isn’t having other issues getting to/from the sensor it really doesn’t matter.
I’ve used successfully with velcro up, down, with the top edge down and with side edges down. Orientation is just a red herring as to why it really worked.

What I did on my last trip was put it in the sleeve pocket of my jacket. The first booth I went through, it went through fine; though I’m not sure whether it registered before or after I took my hand off the bars to point my wrist at the ceiling.

The second booth, no dice. Had to take it out of the pocket and hand it to the attendant. And wouldn’t you know it.. it was in my pocket the wrong way.

Upside down vs right side up is bad terms. It needs to be with the velcro pointed to the sky. Even in that orientation I’ve not had the best consistent luck because around NYC, the readers aren’t even consistent from booth to booth. And the whole camera/plate trick only works on the booths without a gate, if there’s a gate you’re pretty much forced to wait for an attendant if it doesn’t work right away.

I did some work with passive tags, and at least for the particular standards I worked with, the physical orientation didn’t matter. I’ve experimented with the EZ-Pass tag while going through the gate, and I believe it’s the same.