Remounted all the supports for the front ring inside a plastic bag - hopefully this will protect the clecos and help with the sticking of plaster of paris vertically to the under surface.
Add a couple of measures of PoP and rough shaping with a squeegy....
Forming it on the actual plenum does help get the 'proportions' right, but I cleaned and masked up as much as possible, also some release wax on top of the electrical tape.
One potenial problem is the lower shape, probably too much like that and will need 'trimming'.
