I think if you want to stay with the current setup, might be better to ensure two cameras are overlapping and they are using the varifocal system so that you can get as much detail in the frame as possible. A camera on the left corner (overlapping with the right camera) may have been able to capture when the rock went airborne. If you had another mounting spot further right from the right corner camera may have been able to get a better visual of the impact
These cameras are good, but I doubt it could catch a small rock traveling at speed LOL.
Time for Myth Busters to put it to the test LOL.