I think as far as the 'skull' goes, the logit( risk score ) is on the viewers far right. You need to go through the mouth region to get back to risk score. If you are doing it right, you will get a number between 0 and 1. Also you may want to check that inverse logit( logit( a ) ) = a, if you have the right inverse logit function. The formula you give above looks like it is taking odds to probability, rather than log odds, which is what is estimated by the logistic regression model.