A couple of years ago there was a discussion of this on the Widow website. One of the more respected tinkerers there discovered that his MA shot better at a higher brace height, like you are using. He made the comment, which I thought was interesting, that because the grip on the Widow is offset forward about an inch, a 9" brace height on a Widow would be the equivalent of an 8" brace height on a bow with a grip without the forward offset.
The downside to a higher brace height is a slightly higher draw weight and slightly reduced stored energy, so the general rule is to set the brace height at the lowest point consistent with good performance and bow noise.