Think of a pot call as an instrument that is "played" with the striker. They go hand-in-hand in the total package. A great slate won't sound the best with a mismatched striker, and a great striker won't be able to do much on a poor slate.
The actual sound, though, is coming from the whole pot / surface itself... the harmonics of the surface and its relationship to the material it's attached to. The striker causes the vibration. That's why hand placement is critical,holding the pot with just the tips of the fingers to allow it to play without your hand absorbing the vibration and the sound. Finding the sweet spot in the outer area, but not the edge will get you the best harmonics and sound. The center will sound "dead" due to lack of vibration. Same with the outer edge. 1/4"-1/2" in from the outer edge is usually a good starting point to find the spot. Play in different areas until you hear it, feel it.
*disclaimer.. I'm no callmaker. They may be able to give you a better answer.