Twice I walked around with two a LL from Japan and XL of US Regional.
Now the first time, each picked up one different street pass. Second time only one got a street pass. So there is a distinct chance you might miss 1/3 to 1/2 of street passers, although I think most that make it linger more in an area. It’s less a pass and more a linger. Course you’ll be lucky if anything crosses a Nintendo Zone that works. Still it is more handy than PSN’s NEAR.