I have just been diving in thailand (where I live and work) in the Islands surrounding Ko tarutao national park. I saw the most BTA's here I have seen anywhere in thailand. Heteractis magnifica are by far the most common with equal amounts (but alot less) of Mertens, giganteas and cyrpto adhesiums on the sand you will find lta's and haddons (I even found a rare purple crispa this trip).
The Bta's are almost all brown, some have electric green tips and on my last trip I found a small colonie of the most vibrant Red bta's i have ever seen.
They have always been in 10 m or less of water, always as a clone field, in very close proximity to sps corals and hetreactis magnifica anemones, and in this part of the world always with amphiprion eppiphium. Their columns are always buried into the rockwork as seen by aquarists.