So what you're saying is that for a more focused, outward sound, the cab should be horizontal, and vertical if you want to sound to be more dispersed. If this in fact the case, I find it interesting because of an experience I'm having in a particular gig situation.
We have a standing monthly engagement at this one bar. It's small and we're kind of shoved in a corner. I've been using both my cabs (112/210) with the 210 stacked vertically on top of the 112. With this configuration, our guitar players find that I really fill the area that we play even though the overall volume is balanced out where the audience is. Because of this, I started to just use my 112 on it's own which I know to be really focused and the guitar players notice a big difference. However, I do miss the tone I get with both cabs combined.
Although it wouldn't "look as cool", if I had my 112 stacked on top my horizontally placed 210, the sound would tend to be focused outward. And if I decided to use my 210 on it's own instead the 112 for this particular gig situation, it should be placed horizontally.