The heat in the coil is I^2(R).
So assume a coil at 4 ohms and voltage at 12 and the engine just sitting points closed - not running.
4 ohm coil = 36 watts.
1.4 ohm coil = 102.8 watts
4 ohms total, 2.6 ohms in external ballast and 1.4 in coil =
36 watts total, ballast is 23.4 watts in the resistor and 12.6 watts in the coil.
Note 1: It does not matter if there is an actual resistor in the coil or more/thinner primary windings. Same heat - same place.
Note 2: Coils are not running as straight DC resistance heaters. This is a trace from my engine on the output side.
The small peak between ignition events is the points closing again. The actual power dissipated is a bit less. The higher the RPMs, the less heat I am pretty sure. This is why A4s are tough on coils, we run a lot lower RPMs for longer than many other use cases.
Note 3: The Moyer coil and other 4 ohm coils have been well proven to last on A4s. Empirical data is good here
Note 4: I think a 4 ohm coil produces higher voltage than a 1.4 ohm coil ballasted to 4 ohms.