Hello, I'm looking for night sights and strongly considering the XS big dot sights. I'm getting older (53) and my eyes are not as good as days past. So,how big is the dot? Could someone measure the dot, the triitium vial and the overall height with a set of calipers? Are the XS rears tritium or just painted. Has anyone tried them with the std M&P rear or with any rear that has a single tritium dot. I also like the Sevigney 2 dot tritium carry sights. Anyway, I guess I'm looking for a way to use the XS big dot and some other rear with a single tritium insert. Thanks, all. - Pitch