Scaling artwork is very, very difficult, because the work takes as long as the work takes and the materials aren't cheap, especially with oils. What was the overhead on those sales? The hourly rate?
You only have so many hours a day that you can paint, and you can only get so fast while still doing a decent job. So there are a lot of limiting factors on the production side. There's also a ceiling as to how much you can charge unless you're looking at professional level, art-world work, which is a whole other industry.
So I'm not sure exactly what kind of scaling advice you're looking for.