One other tip that might be helpful - the STL file that you use needs to be properly positioned relative to your printer's coordinate system. For example, if the (0,0,0) location is in the front left of the build plate, then your STL file needs to be exported so that this same location is where (0,0,0) is located. The main reason for this is that you won't be able to reposition the model when S3D loads it in the background, so you have to make sure you get it correct from the start.
If you model has the wrong coordinate system, then just import it into Simplify3D as you normally would (File > Import Models), and then double-click on it and change then XYZ offsets until it's in the right position. Then go to File > Export Models, choose Binary STL file, and you can save the file with the correct coordinate system. Use this new file as the <printerModelsOverride> setting.