Well, take a look at Da Vinci's Mona Lisa. She has some dark, yet horizontal (NOT angled) background behind her. Or Girl with the pearl earing, it's all black. Same as Rene Descartes' portrait. They are homogeneous, not angled like yours. Also, some vegetation like the Mona Lisa's could have worked. My thoughts anyways, your work remains your own and it is looking fantastic. Cheers, and happy CHRISTmas