well its not just physical contact that can cause problems, they can also release chemical warfare on each other. On a smaller tank the effect will be a little more than in a larger tank in which the chemicals would be in a lesser concentrations by volume. I have read that carpets are more notorious for this than others. As far as worrying about them ending up in "hand-to-hand" combat - what you said is true. If they choose a spot and stay there for good, it will be ok. May take a while sometimes and so you want to add one at a time (if you choose to add more than one). I'd stick with one rock dweller and one bottom dweller. This will almost ensure that the twain will never meet. So have the BTA either alone, or if you later decide to add another anemone, go for an LTA or carpet (preferably the former and definitely not both)
I have two BTA's and one LTA in my tank. And it doesn't worry me because the BTA's are on the upper end of the rocks and the LTA is residing on the sand bed. There was some moving earlier when my anemones were new and also when my water parameters went askew. But after that they never did move. But there could always be a fateful day lurking in my tanks future.....
I keep dreaming of a carpet but am thinking that a 90G world wont be large enough. Also I would need to add MH to the other half od my tank and then maybe build a rock wall to prevent the LTA and mushroom from ever locking onto each other...But like I said - thats in the realm of my dreams.
