I'm working on a rolling workbench for my shop. I'd like to attach a lower shelf to the 2X4 rails using pocket holes, but I'm having trouble figuring out what to set my jig up for. The 2X4's are vertical, and they will be holding 1/2" MDF for the shelf. I tried setting the jig for the 2X4 settings, but then the 2 1/4" screws are too long, and the others are not long enough. Should I be setting the jig up for 1/2" and then using the 1" screws? Also, am I supposed to use fine, or coarse screws for MDF? I will also be using MDF as the workbench top, built up to 2 1/4" thick, so length of screw won't be as big of an issue as screw type.