With the spread we see, a single ring of the inner Romulan star system would be comprised of approximately 140 outposts.
It's an interesting coincidence in this model that the outpost carrying the number 1 is close to the twin worlds at the time of the episode... A possible further argument for a setup of greater scale and thus greater stability?
The point could also be made that the companion world of Romulus is named Remus in this episode already, not Romii or RomII - making it difficult to explain why those two spots would be close to each other in a map of a single star system.
But the main advantage of the single-system model, the explanation for the impulse reference, is intriguing enough. And never mind that high warp is used in the episode a lot, too. After all, other TOS episodes suggest that high warp inside a star system
is actually really slow.