Xenia is a really fickle coral. Some tanks can't grow it at all, some tanks grow it like a bad weed. It seems like it needs a perfect niche of light, flow, and parameters to thrive. It does like high light and some flow, but not sure what exact params it prefers better than others.
When I started I had a few different bunches of it that did well for about 3-4 months and then shrunk back till it was gone. I now have a patch of blue Xenia that I've had for about 6 months and it is spreading pretty well. I avoided it for years, and the only reason I got the blue was because it was attached to a piece with some GSP'S and an SPS
Only thing I could suggest is to make sure it's in a high light area, with a little flow, and keep your params in good shape.
Good luck with it.