i let craig t clamp his tl's to my 13' bogen at a recent galactic show, with my small diaphram akg 391's on top and the tl's clamped a little lower.
the stand seemed to "lean" a little forward at the tippie-top, but it turned out ok. used some extra duct tape to the floor just in case.
if i had it to do over again, i would put the tl's/large diaphrams on the top, and clamp the 391's/small diaphrams
i could see where lowering the height of the stand would increase stability, also.