I live in a windy location and have found this cowl for windy locations. It is 100m diameter though.
https://www.electricaldirect.co.uk/product/blauberg-external-wind-baffle-vent-4-inch100mm-black-936077?rr=item_page.recs1&rrStrat=AdvancedMerchandisingStrategy&rrItem=0
