Ok, so the starting phase requires some more thought. If the ideal point for the ignition when starting is not the same as either of the edges from the sensor, a reasonably accurate speed measurement is needed to determine the delay for the spark. The easiest, en probably most reliable thing to do, would be to align the rising edge of the sensor with the desired point for the ignition when starting, and to use an accurate solution in hardware and software for the spark timing when the engine is running.

How does this work with the current software? Is it possible to start the engine that way? On motorcycles, this usually isn't a problem, because the sensor is aligned with the ignition point when starting.