I think you're right. I sometimes take 2 Marshall 1936 2x12's to a gig and put both on their sides next to each other, mostly because they both have castors on and would therefore not sit flat on top of each other.
The gig was at a school fete, and we were playing on a trailer in the playground.
I always run my amp on its side! Its beacuse it tightens up the bottom end a bit, plus makes one of the speakers closer to your ear which makes it easier to hear.