I used to visit an art web site (
www.studioprocucts.com) (I believe this is corrrect) where the guy who runs the place promoted the following method for painting a portrait . . .
He positioned a slide projector behind a transluscent sheet on which he projected the image he wanted to paint. He set up a canvas immediately to the right of his rear projected image. He purposely threw out of focus the image he was projecting so that about all you could make out were masses. In a sight-size sort of way, he copied these very blurry masses onto his canvas. When finished with this stage, he would sharpen the image a bit, and start over, laying in some of the detail that now showed through the soft focus. He repeated this procudure until the image was sharp, and so were the detail he was adding.
I believe he had a video of this somewhere on the web site.
I mention this since it is, in a way, similar to mapping out the masses first, a la Sargent, and then working toward the specific.
I doubt that you'll be able to see this on that site nowadays since, for some weird reason, he suddenly decided (a couple of years ago) to make it a pay-site and, to my knowledge, most of his following found other sites to go to.