Just received my new Titleist 913D2, 10.5 degree with Diamana S+ 62, regular flex at standard length. It has a swingweight of D-2. I thought standard swingweight was D-4, or close to it. For me D-2 seems light. Is D-2 the standard swingweight and if not, what does it mean about my head. Purchased from TGW so not worried about seller. Thanks