If you are having trouble with the swing, try to do it in a reversal way instead of missleg. That means let your swinging leg touch down briefly before you swing into the masterscoot.
You can reach over sideways or even fully inverted. It depends on what you want to do afterwards. If you want to swing or pop into a straight backflipping trick, you may want to perform your masterscoot with a lot of inversion. If you are going for more off axis flipping tricks, like corks for example, you may want less inversion.