Xtracrylix are a dream to spray. I usually thin them with a homebrew thinner: 2/3 de-ionised water, 1/3 isopropanol, a dash of Winsor & Newton's flow improver and slow drying medium (glycol and washing up liquid can be used instead). Have never had any problems with covering.
One caveat though: they need to be properly stirred. I use a paint shaker, let them shake for at least 5 minutes.