Yep, as valve & seats wear, their contact area ring increases in width. This spreads out spring-force and lowers pressure at contact, leading to less sealing. Lapping further increases this contact area. FSM dictates minimum & maximum seat contact width. Aim for the narrow end of range first with valve-job machining (3-angles). Then lap just slightly to improve sealing.
With modern machinery, it's not any more difficult or expensive to cut fully-radiused valve-seats. Then cut flat seating area of minimum width to preserve improved flow. Much, much better than 5 or 7 or 9-angle valve-jobs. Also beryllium-copper seats shown transfers heat much, much faster than steel, reducing wear and greatly enhances exhaust-valve lifespan.