You know how it is, open the roof and pour a little water into the channels, then go and check it actually runs out of each corner correctly. Best to check / sort this now rather than when its flooded, I'd call it preventative maintenance really.
I pour a bit of water into each channel and wait, nothing happens at all. I pour a bit more in. I then notice a torrent coming through onto the drivers seat
The error here is I was expecting it to have drain channels to each corner via pipes, but it appears this design of sunroof actually seals the glass to the roof. Usually the ones I've looked at before allow water to pass sometimes and the channels drain it off.
I guess the clue here was the rubber seal around the glass instead of a felt (kind of felt material) seal...