Different variations definitely have different sized discs... and no, not referring to palys, even just within zoas. There are some little zoas and some bigger fatter zoas. I've not experienced the stretching neck except for the occasional one positioned where it is reaching for light (like one that is down between rocks) while the rest of the colony is happy to keep their necks shorter.

A friend and I bought identical frags from the same seller. He looked at them in my tank and commented how much longer then necks are on his. I saw them in his tank and definitely agree. In my tank they are under MH light (same as the seller had them, just different wattage) and in his tank they are under PC lights. So that is consistent with what is being said here.