Mine are bynecessity.
I run a pair of 485's(now 410's) and they don't fit under the tower and being 6'4 I would be nearly eye level with them while standing up.
I wasn't pleased I had to, but it's growing on me.
Had 2 of mine on top for one summer then moved down.Kinda looked like those jeeps with big oversized lights on top of roll bar.Only reason to put them on top is if you run outa room below and want even more speakers.What about mounting partway down tube on inside.
I have to have mine on top as well... Had them below to start with but after smacking my head one good time, they got moved quickly. Its growing on me a bit and it makes it much nicer to be able to walk around and not bend over.