How are link hint characters used?

[MaxG87]

I am using Vimium and a non-standard keyboard layout, Noted. Therefore, the default link hint characters, sadfjklewcmpgh, do not fit. Initially I replaced them 1:1, e.g. c for a as Noted puts c where the key a is. However, with this mapping I get both u and ü, which sometimes are impossible to tell apart. So, I want to improve upon this.

Now I wonder: How does Vimium use these characters? Why, for example, is h at the very end of the selection, and f, the strongest letter, in the centre? I'd like to understand that to find better hint characters. Is there any documentation I missed?