Wong Teasers

I have a question regarding the Wong Teasers. I understand the concept of the 1.5-2.5 dog up thru the key numbers of 3 & 7. I also understand bringing the 7.5-8.5 favorite down, also crossing the key numbers 3 & 7. Here is my question: Why does the Wong teaser not include the 7 pt. favorite also? It's crossing the key number 3 as well as 2,4,5,6 and if the favorite covered by 7 or more the leg is still a winner. Your betting the favorite so any win outcome greater than 1 is a win. It dosen't cross the number 7 but it includes it.