At Upfest 2016 there was one site where there were about thirty or so of these smaller (metre square) boards. I rather like seeing some of this smaller street art, which tends to have a bit of a crossover with fine art, perhaps exemplified by this portrait by Lauren Maria Hill.
This young Bristol artist appears to focus on portrait work and seeks out commissions and freelance work on her website. Her images, including this one seem to concentrate on the face itself with great detail, leaving the surrounding hair as a complementary feature, but somehow separate from the face. I like her work, and hope to see more of it around Bristol.