But it's not perfectly linear, and as should get bigger, the incentive to optimize grows

Not exactly. A diesel engine uses less fuel at 80% load than 50%. At maximum load it uses the most fuel but in general as load increases the engine gets more efficient and so the calculations are weird.

Note that generators need to run at constant rpm to provide the correct ac frequency. Your car has gears so that it can run at lower rpm at low loads and so you won't see the same effect.

An independent diesel generator could have been loaded onto the ship as easily as the spy equipment. It was a tanker, there was plenty of room for a genset and its own fuel. Then the ship's power plant wouldn't be taxed at all.

Then you have radio equipment in addition to an independent diesel generator and fuel to explain…

Yes it was a tanker. The bigger the ship doesn’t mean it has more people or more power generation like a cruise ship. A tanker has a crew of 4 plus captain, maybe?

You've got the spying equipment to explain if boarded. An extra generator is hardly a concern. If anything an auxiliary generator can be explained as a backup/replacement for the ship's mandated backup generator.

Generally the people ordering radios don't think about that. They are used to land where you have more power to the building than you could possibly use.

Less fuel less efficiently