I think its just a terminology problem here. A stacked configuration is 2 identical Bowtie Reflector antennas mounted one on top of the other in the exact same direction with the bottom of the higher antenna's mesh touching the top of the lower antenna's mesh, with the output feeding through identical baluns over identical lengths of cable into a combiner (and preamp since this is typically a deep fringe solution). When I say identical, I'm not kidding.
Yagis can be stacked too.
Crispy, you can mount them on the same mast in different directions but I would keep their mesh reflectors about 1/2 their length apart, so about 17 inches from the bottom of the higher one to the top of the lower one. Never mount them back to back or they will tend to cancel eachother out.
Like Yaamon has found out in the past, its a long process of trial and error to get the patterns to work together.