The problem with a carousel in wargaming (as opposed to dioramas or railroading) is that I don't just want either:
(1) A big, decorative piece of cylindrical blocking terrain
or
(2) A small, decorative piece of cylindrical blocking terrain with a larger cylinder of ornate terrain that reduces ranged combat effectiveness.
I want figures to be able to run through it, dodge back and forth amoung the horses and carts, and have lines of fire and movement open and close in interesting ways. To do this, I need at least two annuli where figures' bases can fit with one ring of horses between and one on the outside.
Really, to do this, you have to compromise and use two rings of flats for the horses. Also, don't put polls on the tops because you don't want to have to reach down between them to move figures. Even without polls, the horse flats need to curve along the ring or they will gum up figure movement.
So what we want to be a fast=paced, dynamically exciting game of dodge and dash becomes a fidgety-widget, time consuming drag. I might as well play [insert your own opinion of a game here]!