Den Phal pleated growths - underwatered?

[mexicowpants]

The newest growths on one of my Den Phals look kind of pleated like this:



Is this a sign that it needs more water? Or are some Den Phals naturally like this? I water it the same as my other Den Phals, but it's a LOT bigger and in a faster-drying medium (gravel as opposed to red lava rock). It has lots of new root growth on it and otherwise looks really healthy.

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