Thanks to all the above: required reading for those who are fed up with 1 mm tip on 100 mm gauge.
I went for a 200 mm funnel to bring the modified tip down to 0.25 mm (cp European Davis 0.2 mm) and it worked beautifully today: OS console 44.2 mm, WD shows 11.1 mm, CoCoRaHS 11.2 mm. (Good vertical rain for checking, not much wind.)
P.S. OS WMR200 manual says the rain gauge can handle 9999 mm/hr: I make that 2.78 tips/second (and I don’t believe it - I think they mean the console display!).