It appears my glaziers don't supply this type of glass - hence I wasn't aware of it.
Yes low sightline is what I've been after - I can then replicate just without the sliding sashes. I'm thinking of it as a piece of art rather than a window which I appreciate is a bit odd but then it's the clients choice.
Making the curved glazing bars is my next issue - would you have three panes or 'stick on' for the top section?
I'm imagining a jig for an arc cut across the router table to profile (and haven't got my head around the tenons yet!)