Rate them however you want. It only makes sense that you'd give high ratings to games you own, you bought them because you like them. 2 and 4 player games deserve different ratings, at least they'll have different art. I don't know how the top 100 works but its a little wonky because EMs get WAY fewer ratings. Do your part and rate as many as you can to fix it!
The only problem is when someone gives every game they own a 10 or every game from some company a 1.