Fascinating, it really does sound like him!

I’d be interested in hearing the variants you came up with. It’s also gotten me thinking about other lines for that scene. The trouble with it is that if the Falcon isn’t in Hyperspace in the next scene, there’s really no place that it could be that feels right. It can’t be still escaping from the Death Star because the tone of the scene is very much that they have already escaped and can breathe easy, nor can it be that they have already traveled to the Yavin system because they are talking like the escape was only moments or at most minutes ago.

But here’s an idea: What if the Falcon went into Hyperspace immediately after escaping the Death Star, only to quickly drop back out of Hyperspace and calculate a new course to Yavin? That would make sense because in ESB it is established that a ship can be tracked to its destination based on its course entering Hyperspace, so a multi-legged journey would be implied here. It also would explain why Han seems so cocky about his escape and his conviction that the Empire can’t track his ship, since it’s making multiple jumps to get to its destination.

Vader’s line could be:
“They’ve made their first jump through Hyperspace”
or
“They’ve completed their first jump through Hyperspace”.

Now we can have the next scene happen moments after escaping the Death Star while Han waits for the navicomputer to give him new coordinates. In fact, with this concept, Vader’s line doesn’t even need to change, but the change would at least hint that this multi-hop technique is being used.