We see this over and over on big cammed engines. The engine wants timing at idle to be somewhere north of 20 deg but the engine will not start.

So the timing is pulled back to allow the engine to start but the torque at tip in is reduced, it doesn't idle as good, throttle response is reduced and the mileage falls off.

Vacuum advance or computerized ignition control is the only way to have both.

For ignition timing you need to control at least 4 things, timing at cranking, idle, cruise and wide open throttle.