what the engineer told you was correct but can be described differently. during the time between firing the coil is energised, when it needs to fire the power to coil is momentarily cut which creates a large magnetic field which is transferred from primary(coil winding-ignition wiring) into the secondary(coil winding and through spark plug). if the coil isnt powered up long enough before firing due to very high rpm then the magnetism in the coil will be reduced and spark will be weaker. also low voltage will do the same even if it has time to become fully saturated/magnetised
and as for spark plug gap im 99% its due to combustion chamber pressure. electricity cant travel through dense area as easily but i cant remember exactly why anymore if 1.1 works and doesnt miss should be ok but many or most people us slightly lower to ensure correct spark even if its not quite as big.