I like to get a nice and fat base vs a tall and skinny piece. Once the coral gets huge, there will be a trunk for it to rest on vs a skinny base that can break easily. If you glue your frag down sideways the base will grow out wider than upright. On a 2" tile, you'll have 20 branches growing out of it around the same time that you'd have only a few if you start out upright.
Yes, I thought of the skinny stem as well down the road. The idea would be if this worked, then in 6 months or so to remove the frag, cut the stem, and permanently mount the hopefully by then mini colony. This way the frag would have already started to grow up and outwards before starting the base. Just looking at a potential idea to get quicker growth starting out the gate than waiting the long wait for the base to establish.
Just a thought.