I just installed an exterior pre-hung door a few months ago. The frame was installed level, flush and plumb and ostensibly should close perfectly. Our house's outer walls were built onto with 1" poly insulation board and aluminum siding. The long screw that you use in the top hinge, to pull the door true, falls exactly where the foam siding is, and just spins freely. In other words, there is no "meat" for the long screw in the top hinge to grab onto. So, even though the frame is level and even, the door itself has a slight sag to it. Any solutions to pulling it more true, without using screws to pull it from the hinge area? Thanks!