Back to the drawing board, I’ve had 2 days off work so began marking out the teeth of the foam mats onto the polystyrene sheets.
Results total failure, I tried the hot wire first ended up with the edges beveled and gaps to wide, next attempt was with the hot knife edges were much better but still to big a gap when joined.
So back to the drawing board, I was hoping to use the polystyrene to give a little extra thickness and hopefully a little more rigidity to the tiles and also to cut in rivers to give them a depth.
As is I might try using the hot knife the carve out a channel at least a few mms deep and try that, as for the polystyrene that’ll be used to provide hills at least for my 6mm.
The best layed plans of mice and men oft times go astray 🤪