A non compressible media would be one with out peatmoss, coconut coir, soil would be my take on it. A media with pumice, Turface, Quincan and such would not compress.
The thing that would make it more true is if the top was enclosed the same as the sides of a pot. As long as the media can be displaced upwards, the roots would continue to grow and slowly raise the plant up if not breaking the container.
When you see them on Socotra and rocky terrain, where they are growing in a crevice, then you can see how the caudex is growing ontop of the ground and developing larger.
I think when we talk about the caudex, it is quite conveluded. If a plant was left with never being raised. We would then call what was above the soil line the caudex and what is underground the root system. The present root system, then becomes the caudex when raised.
In light of raising or not a plant as it grows will become larger in girth, but some more so depending on it's genetic make up (some fatter).
My thoughts on this subject.
Rick
