===== How does an SCL’s Fuel Penalty work? =====

I don’t think it does.

For each SCL in AirData >> AirExecutionFactorsData >> AirPackagesData is an element for Fuel.  The design originally was that each SCL could "cost" a certain fuel burn rate (some munitions cause more drag than others).  Envisioned in the original design was a provision that a certain SCL could have a //negative// fuel penalty (in other words, an SCL could possibly contain auxiliary fuel tanks).  Neither one of these has been fully implemented.