IMO/E hosting is never a sure thing. However some factors that increase or decrease your chances for success are, weather the fish are wild caught, aqua cultured or tank raised.
I have read theories that an anemone hosting is a learned application. Tank raised anemone fish, seem to take the longest to want to reside in an anemone. Aqua cultured have a slightly higher success rate while wild caught seem to have the highest. Although there are scenarios where that theory is shown to be false, the majority of the time from ME it seems to hold some validity. I have a wild caught sumatra perc, and a tank raised ocellaris together. At one time I had only the sumatra perc, and my RBTA, the perc would not look at my anemone. I added a wild caught true perc about 3 months later, it took immediately to the anemone. In a day the sumatra perc threw the TP out and took over the anemone for herself. The TP died (another story) but, the Sumatra one kept her anemone, and when I added my tank raised ocellaris it only took 2 days for it to take to the anemone. Prior to that scenario in the time my tank has been running I have had 5 tank rasied ocellaris, 4 orange and whites and 1 black and white, none wanted my anemone. Out of all the wild caught specimens I have had all but 1 took to my anemone within a day. 4, true percs, 3 B&W saddle backs. This is just based on my experience and I know there are scenarios that contradict mine but if it will help I thought I would offer it.