Erik,
It's accurate - the 18" driver is mounted on the face of the front baffle, so it will be time aligned already with any other "conventional" (front baffle loaded) top cabinet. There is the rear horn, but the first wave of energy out of the sub will be that off the front of the cabinet. This is what you hear first, the lower frequencies produced by the rear horn are close enough together with that of the front face that the human ear can't perceive any delay difference between them, merely that it sounds "fuller" than if the rear horn weren't there.
BTW: it's a GREAT peice of equipment for the money. I've got some and love them!!! I power them with bridged RMX1850's.
ScottH