Nerds_feather
Purveyor of Nerdliness
Most of the authors in the Baen stable would be considered mid-list. Even Lois Bujold mentioned that she didn't make a reasonable income from her titles until she wrote at least 10 books.
My sense is that the Baen catalog sells well over time--or, to put it another way, they have a "long tail." But I don't think they have a lot of fast-selling titles, and I'd imagine--as with all the other SF/F imprints--the majority of authors they publish don't ever move big numbers.