It's a bit of both I would think, as I believe the "ships",
NPCs, that you kill scale with your Rank. So, and I not totally sure about his, someone that's
Harmless is not going to meet up with the same NPC ships in a RES, as someone that's Elite. At least, I think that's how the game works. When I was grinding Admiral in SOTHIS/CEOS..., at "Dangerous" in Combat, the game tossed Deadly Anacondas at me, for the Deadly and Elite level, data delivery missions, sometimes as many as 4 of them at one time! I think the game might actually stay slightly
above you, tossing a challenge at you. I don't think someone at Mostly Harmless doing those data runs would have encountered the same level ships, but I could be totally wrong about that, but I have noticed, that as I have gained in Rank, so have the ships I've encountered, even in
Low RES or just NAVs. Could be totally wrong though