Modern ignition systems have dynamic coil charge (dwell) times.
This results in a uniform spark delivery at all loads.

The ignition amp on a cossies for example when told to charge the coil,
will drive the coil negative to zero volts putting the full 12 volts across it.

This results in a current of about 10 amps to flow.
This situation is called saturation.
If this condition stayed, the coil and amp would burn out in seconds.

After about 3 milliseconds, the amp backs off the drive, raising the coil
negative voltage nearer 12 volts until it measures about 5 amps
going to the coil and then holds this level.
This will NOT produce a spark even though the coil voltage across it
could have halved or more.
This is because any emf produced is absorbed by the current flowing in
the primary winding which reduces the secondary output to a point where
it is unable to spark.

A sudden release of the coil negative to an effective open circuit produces
a strong spark from any of these points in the charge cycle due to the
magnetic field being saturated given it has had time to build up.

If you reduce the drive voltage slowly to the point of open circuit then
no spark would be produced but this depends greatly on time
and coil design.

The off state is open circuit.

So the cycle is...

OFF
CHARGE FULL POWER FOR 3 milliseconds ish
REDUCE POWER to 5 amps
SUDDEN SWITCH OFF generates spark