Coil voltage

The GM HEI module has an important feature for high[er] rpm engines that the CH ECU does not have. So along with not requiring a bal res, the GM unit has variable dwell. The Ch unit has fixed dwell. You need a lot of dwell for the coil to fully 'charge' at higher rpms, & the more cyls being fired from that coil, the worse the problem becomes. Dual point dists were used in the old days as a fix, but not much good. More cyls, less time at high rpms to charge the coil & result is misfire.
With fixed dwell, the dwell is set for max rpm anticipated to ensure coil charges fully. But at idle & low rpm, with all this dwell [ coil has current flowing through it during the dwell period ], coil gets hot. Long dwell is not needed at lower rpms. The GM module reduces dwell at low rpms & keeps the coil cool; it extends dwell at upper rpms to ensure coil gets fully charged with current.