I got about 20 minutes on finally so nipped to a RES. I need a little more engineering but a thought occurred: the biggest wanted guy I shot was a Krait. I've never seen any large boats.
Is there a specific scenario as far as RESs are concerned for large vessels to show? Or is just RNG?
It is largely RNG, however High and Hazardous are more likely to produce bigger high value targets in my experience.
I recall reading that if the first pirates to appear or low value targets then you are unlikely to get anything large or valuable spawning so it could be better to cruise away then re-enter the RES for something more interesting.