I paste approx 13 minute youtube tutorial link to a guy who has another method to line up the masks in Speedgrade (maybe similar to nesting method). The method is between 5:25 and 7:47 and goes something like, your Premiere Project original video size has been cropped and your SpeedGrade mask is being applied to your original footage size, not your trimmed size. His fix is to apply the transform effect above the lumetri effect in Premiere.
I have not applied it, he demonstrates it better then I can describe it and works for him.
This is the link and is called Adobe Premiere Pro and SpeedGrade Tutorial | Using Masks For Vignettes And Other Color
