My personal experience with xenia leads me to believe that xenia thrives with lots of light. The amount of light you have should work just fine, but sometimes it doesn't hurt to have a little more light. I have the same tank and I love it. I put a 32 watt smartlight on it. I used the hood that came with it, took out the existing light and ballast and in the same light hood cover that came with it, I installed a 32 watt retro kit that I bought for 52 bucks from Petwarehouse.com. The tank looks sweet now. I have just a really large carpet anemone and two clowns with some calerpa and a piece of live rock. The carpet thrives with the added light. It was half the size before I added the stronger light.
Also make sure that you add Iodine, or at least do water changes pretty frequently. Doing one or the other should work just fine. As with the lighting I have also found that Iodine is very critical in having thriving xenia.
One other thing is that some corals do wierd things sometimes and they usually pull out of it. The xenia that I keep in my main tank sometimes just shrivels up for an hour or two and then opens right back up. It almost seems like it is part of some process or maybe something agitated it, I'm not sure, but it always comes back around.
Have fun
Gary