Thank you! :D
The similarity is calculated on a per pixel match basis, so the positioning matters, though I'm thinking of creating a full game for this in which I would make that part more sophisticated. :)
Also if the score was unexpectedly low but you did draw in the right position: for a bit there was a bug in the web version of the game where on some computers (not each one and also not based on the browser, very weird) it only counted white pixels, making it incorrect, but it has been fixed a bit ago