Definition of "secondary screen"

I’ll begin by saying that I’m not sure if this is a bug or a feature. I frequently work with Scrivener on two monitors in full-screen mode. I have the preference to “open full screen window on secondary screen when available.” I typically understand “secondary screen” to be the screen without the menu bar. It seems that Scrivener understands “secondary screen” to be the screen where the Scrivener window is not currently located.* Is this the way it’s supposed to be?

*Actually, I think the exact definition would be the screen where less than 50% of the Scrivener window is located.

Yes, it’s the screen on which Scrivener isn’t primarily located. I suppose I could change the wording to “other” screen…