It depends upon how you want to use those points. If you want to stay at AKV every other year, and want to have the ability to book during the 11 month window there, get the add-on there. For instance, if there is a room you want at AKV every other year that takes 150 points, you can buy 75 points at AKV, bank and borrow every other year to reach your total of 150 needed for the reservation, and book it during the 11 month window.
If you want to stay primarily at OKW then add on at OKW.
If you do not plan your trips until the 7 month window, it doesn't matter where your add-on points are located. Just be sure they have the same use year, so they can be easily blended ay that 7 month window.
If buying through Disney, and not resale, they will have the same use year.