I was giving that some thought, and even started to hypothesise why in the last post but thought better of it, but now I guess I'll share my guess. Now I'm sure the 4cm that you found was most likely an average, and in most cases there is usually an exception to the rule. In our tanks the temp usually stays more constant as well, and if its warmer, it is possible that they will expand more or shrink more, who knows
. Perhpas it is responding very well to your lights or water conditions.
In the end right now all I can do is guess, still can't say for sure if it is a Waratah or not, but I'll keep looking around and help out if I can.
Thomas