I presume that you are talking about wind interference, not pitch problems. A cross wind can certainly play havoc with whistle playing and I have always found that the moulded plastic mouthpieces, with deeper channels, were better than any of the full metal types. I noticed that on "Chiff and Fipple" one of the makers of plastic large whistles (Cook?)had added a low plastic wall around the top and sides of the whistle. I suspect this is both to improve the volume and to keep away cross winds.
This looks to be a good idea and, having got back into whistle making, after a 34 year gap, with a PVC deep "D" ... made last weekend to explore some finger hole placing alternatives, I am going to do the same to the next whistle I make (this weekend?).