Zoas are like that. I had one that didn't open up properly for like months and is now showing some faces. You might want to check for zoa eating nudibranch just in case. Zoas come from wide variety of places at wide variety of conditions so unless you are particularly sure about it, you will have to experiment with its position (but not too often; maybe once a week...not sure about the number).
I presume you got an aussie zoa over there? They are particularly very picky about acclimating to the tank and their location.
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You wouldn't want to see my tank. I don't use fancy equipment and I am a noob 
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