I played an online match today.  One of my allies who was flanking me got knocked out by a scout rush, so I built up some defenses to guard to guard that flank.  The attacking fleet was not that large; again, it was mostly scouts (about 45 of them, also had about 15 assailants, 3-4 carriers and an eggship).  My defenses consisted of a full combat/defense upgraded sb, a few hangers, and some repair platforms.  He attacked while I was helping another ally, this one on my other flank, so my forces were elsewhere at that time, and I thought that my defenses were more than sufficient, and under normal circumstances, they would have been, so I didn't bother to send anything that way.  When I checked in on it a few minutes later, the enemy fleet was high above my sb, where it could nibble at it without the sb firing back.  I went back and viewed the replay to see how that happened, but that didn't shed any light on it.  The fleet was moved out of firing range of the sb and was given a few move orders until the move order went high above my planet.  In my experience (and most everybody else's, I would assume), Z-axis in Sins is very limited, almost to the point of not even being there for all intents and purposes.

The fact that the sb couldn't even attack the fleet is an indicator that this isn't even supposed to be possible.  If there is no Z-axis control in the game, how was this even accomplished?