I've not yet managed to work this out (as it does not seem to be consistent) but perhaps I'm missing the "key" to the way it works.
Just how far can you sink a prim (or mega) into the surface of the SL ground?
Someone said the centre of the prim cannot go below zero metres, and that sounds resonable, but is that the case?
I don't think it is.
I made a rock sculptie (on a megaprim) and where I am I can sink the whole thing into the ground (mainland near water)
I gave this to a friend (they live on a hillside on an old sim) and it would not go into the ground very much at all.
Also I remember when I had an openspace, I used to slide some megaprim rocks around and as I went over hills on the terrain of the sim, the rock (max depth) would raise and fall with the terrain.
So it can't just be a set sim wide figure.
Does anyone know?
Thanks.