Although the extra height gadget for the WH40 is not proven in my view it does no harm. I fitted one recently and my rain readings do seem better in some recent heavy rain we had, although this is anecdotal at present I get the feeling it was better than without it. There's no doubt in my mind the funnel on the WH40 does need a redesign. Also I'd go with a WS80 rather than the WS90 as the haptic rain sensor seems to me to be not very reliable or easy to set up currently, just my view....
Stuart