I think the overall height/width ratio of MA3 is approx 1:3.2 (I'm sure someone will correct me if I'm wrong).
Therefore, with the full height present, there is only enough width to cover approx 2.5 5x4 monitors. (Allowing a small amount of scrolling).
It will not cover three monitors, and therefore can not scroll when spread across three screens.
It looks and works fine on my two (5x4) two-screen set-up.... And it will scroll, (if I want it to!
)