I'd appreciate it if somebody could have a look at my thoughts and comment on them. I need to explain the difference between the following sentences:

(1) I was sleeping until you came
(2) I had been sleeping until you came

I think (2) implies a longer process.Perhaps I woke up because you came.
(1) only says I was asleep at some time before your arrival.

Would adding "for 2 hours" make (1) sound fine too?

Thank you!