I don't think it is a size thing. I think it is a way they reproduce or spread - or at least that is what I think. I've had my hand in the tank, cleaning, hitting them accidently next thing I know the next day there are pieces everywhere. Nothing really makes them mad per say but they do have a way of breaking off, losing a limb, float around, and grow elsewhere. You can pull them off and if you don't epoxy or glue the base you just tore, it will grow right back. I have a Jebao RW4 right next to large groups of them and they are fine.
Very hardy stuff and I've found difficult to eradicate. Not that I'm really trying to but when I see floaters about I just pick them up and flush them. No use really trying to re-sell to the LFS unless it is a big stalk or they are 100% out of it. If they are out then sure, I'll take them a bag full.