I don't know if it is environmentally caused or there are two varieties of haddoni, but I have notice differences in structures as well in different individual haddoni. Some will have longer tentacles that seem to be less dense. You can see the oral disk though the tentacles. Others will have very short tentacles that are so dense that there is no room between them at all. In addition, the later anemones seem to have a thinner oral disk if it were to be viewed in cross section.
If you click on my "red house" there is a pic of a blue haddoni that represents the longer tentacled variety and bright green haddoni that represents the shorter tentacled variety. Unfortunately, neither of those anemones are with us anymore.
In my limited experience, it has seemed to me that the longer tentacled variety has been accepted more readily by non-natural symbionts like percula, ocellaris and skunks than the short tentacled variety.