Absolutely nothing at all to worry about my friend. They will not only extend to compete for more light but they will often extend to catch the current. Seen it hundreds of times in my tank and others. They will also extend to feed upon particulates in stream, zooplankton, DOM (dissolved oragnic matter), bacteria and sometimes live food. And last but not least, polyps will extend like crazy in optimal conditions of which I have seen few reefers achieve. I've known only one reefer who achived 100 % daily extention of every single polyp and colony in his tank. Not everyone will enjoy seeing this, but I do/did. He had 4 return nozzles, one on each top corner of his tank spraying inwards on 4 to 5 seconds intervals if I remember correctly. There were hundreds of polyps swaying in the current all day as each nozzle directed them. I myself have seen polyps in my own system which were short and stubby, yet extended for reasons of their own a few times a month, only to decrease back to their normal size.
Again, nothing to worry about, just wait until you see them close for no reasons you aren't aware of for a full week. Just wait, it will happen. See my thread entitled, "25 reasons why your polyps won't expand"
Good luck.
Mucho