I do remember seeing that chart at Mousesavers, and you did read it wrong. Basically if said:
5 nights: 1 night free
6 nights: 2 nights free
7 nights: 3 nights free
8 nights: 3 nights free
9 nights: 3 nights free
10 nights: 3 nights free
11 nights: 3 night free
12 nights: 4 nights free
13 nights: 5 nights free
14 nights: 6 nights free
Once you get past 7 nights, it starts all over again, until you get up closer to 14 nights to get the most savings. Also, I believe you can only book the FT for 8 or 9 nights, if you need more Mary recommends booking two packages.