from what their site say 4% is just that 4% more timing. so what ever your timing is set at its adding another 4% to it.
The spark advance or retard percentages are based on what is currently in the vehicles timing tables. So if the timing is 24 degrees and you add 5%, your new timing will be 25.2 degrees. As for the base timing this is going to vary, even in the same model of the same year vehicle because of the large number of calibrations that are made for each vehicle. If you are wanting to know the factory timing of your vehicle you can data log this with your Predator before you install the Performance tune.