...and with Heavy freighters?
...and with gunboats?

...is there an article in the guide that I missed and that answers this?

Capital ship skill = super capital ship, capital ship, frigate, corvette
Fighter/freighter skill = the rest (including heavy freighters and gunboats)

I think this could stand to be clearer in the skill definitions. I will edit them.

Ah, thank you. I always thought corvettes were freighters and then got wrong results in the navcomp. :D