Briliant - thanks.
I had assumed when talking to the students that is was probably a bounding box issue, as I had seen something like this in the past.
I have loaded the script to enable a class in a couple of hours time.
First thing to notice is this load error which I need to investigate:
Second, is that the cap the volume command in the script is no longer necessary?
I had assumed that to model the shadows etc from the surroundings, I did not need to cap the volume of the context - but I take the point if that context is part of the CFD, then it should be solid?
m