Will goniopora keep growing without surface?

[Bitcoin Reefer]

I'm wondering if I need to put my goniopora on a rock or can I leave it on sand and will it keep expanding its own skeleton? Or is it more of an encruster? At first I thought it had maxed out on whatever rock it was growing on, but then I saw some videos online of propogating them by cutting through their skeleton, so now I am thinking it will just keep growing and I don't need to give it more surface area to grow on? It was a video similar to this one:
If the answer is they don't need a rock to grow onto, then I'd also be curious, CAN they grow onto a rock?

Here's a pic of my guy from months ago. He's grown quite a bit since this

 

[Lavey29]

All mine are attached to rocks