I would leave it where it is positioned, pics of said acro? also lighting? a behavior of LPS corals and octocorals is to expand more to absorb more light, I wouldn't be surprised if some acros dont do the same.
Daytime polyp extension is only a "decent" indicator of coral heath with Acropora, I have observed good day time polyp extension on some acropora that were STNing while working professionally in the hobby. A good sure sign Acropora are happy is if they exhibit nocturnal axial corallite polyp extension regularly.
Growth of course is also an good indicator. The (Nocturnal Axial Corallite Polyp Extension) is a pretty well known belief among old school "acroholics", and I have witnessed it. When I worked for a LFS in college I saw it with my own eyes, The imported wild colonies that we got in, if they exhibited the (NACPE) right before the actinics kick on you knew they were stabilized colonies, ones that chronicallly didn't exhibit NACPE usually bleached, RTN or STN.