Mine stayed and filled the rock low in my tank. Always stretched up and long tenticals. The one moved to the highest point between the two lights and stayed flat and bubbly. Only anemone knows whyNow my mind wonders why did original stick in its current Spot? The spot works for it so does a nem have a min requirement that once met says forgetaboutit I ain’t moving no more or just something different between the two that wasn’t quite identical. Fascinating creatures to be certain now to wait for the 2nd to split and see what becomes of a third nem! Your going to need a bigger tank!
Edit Jinx posted and saw your above lol
In my opinion, the key to making an anemone stay put is having a secure hole or crevice for the foot. This is especially true for BTAs I believe which tend to live on the rockwork. I posted this before and worth repeating. The original sits in the crevice in this rock
When I purchased my live rock back in 2018, I saw this in an invert display tank and I had to have it. I just knew an anemone would never leave the security of that tight hole and it never has.
They do prefer a crevice to bury in and seem to like them to split. Mine would move to areas with bigger holes or more 90 degree angle to split
interesting beast
one day you will come home and this will be your FTS