They are much more sheltered as well. South Wales is very bad because the Atlantic funnels up between Ireland and Devon/ Cornwall. Very shallow water doesn't help either. You have to go about 400 miles SW off Ireland to get into proper Ocean depths. Places like Tenerife about a mile
Im familiar with the North Atlantic and the swells it throws in towards the Bristol Channel, Ive experienced them bashing ore into Port Talbot and in a yacht enroute to both Cork for a weeks racing, also on a rather unpleasant trip towards the bay of Biscay en route to the Canaries.