I've wondered the same thing myself but just come to live with it. lol
I've used LW for a few yrs & it's just part of how it works. Under artist search it will most likely show up with the most commonly found of those files belonging to the artist. What you can do is ... once your search results come in ... if they have chat enabled then there's a reasonable chance you can browse or direct connect to them. So then you can see if they have more files belonging to that particular artist. This is a very handy technique to get a hold of certain files. To do it you should have chat enabled (for some reason it seems to make browsing easier.) To learn more about browse host & dc see:
How to Direct Connect, Browse & Chat As for the logic behind the way the search works ... it's probably a bit technical & I can't I'm not sure.