most of those small
Christ portraits I'm afraid are copies from copies from copies from earlier icons and those are Greek
You need
bit expertise to make difference what is original idea or accomplishment and what is just routine copy from an earlier masterpiece...
Russian 15 cent -18 cent. iconography is not
Byzantine any more, you might find brief similarity but it is totally from different world.
But like Vercingetorix mentioned you can find direct links from Balkan countries and as example take some 16 cent. icon from
Bulgaria than take Russian 16 cent. one and compare them with 13 cent.
Byzantine icon - than you see what I mean. In 15 century
Russia was so much influenced with
Italy and renaissance (Aristotle Fioravanti and Cathedral of Uspenski in Kreml for exmpl.) that you must be blind to not recognize it immediately; while Balkan ... you might know the story with Ottomans and Co. = equal stagnation