Just exchanged emails with Fltplan.com's customer service about FSX loaded flight plan plotting onto the app and position following on IFR plates and airport diagrams. Here are their responses:
Can the app plot my loaded FSX flight plan?
"We do not have a feature like this in our app. You could go to MAPS -> EDIT and manually enter your route you have in FSX and hit SAVE ROUTE. No you won’t be filing with the FAA. You can even enter routes in our website and they don’t file with the FAA until you are approved to file and push a button asking us to file the flight."
While I am flying in FSX while using the sectional map in the app and then switch to the appropriate airport approach procedure plate, will the app follow my progress on top of the IFR approach plate also? How about ground taxiing over the airport diagram?
"Any charts or diagrams that are geo-referenced will show your location. If a file is geo-referenced you will see a green checkmark indicating it’s downloaded on the right and on the left of the checkmark will be a purple arrow."