The WSOP policy this year is:
When 12 or less tables remain in a tournament, play will hold when there are “ TWO “ or more seats available.
WSOP policy has been that for a number of years. But only in specific instances. 12 tables is brought into play with more than X number of players in the field. Used to be a field greater than 1,000 was our guideline, now it's just greater than 20 tables. The rules don't specifically cover field size except for how we balance if there are more than 20 tables remaining in the field. The general rule of thumb used in most tournaments is how many tables get paid? Don't use the WSOP as your basis for this. Our fields generally range in the 40 to 400+ table range. Quite significantly larger than your normal 6 to 10 table tournament at you local casino. If you do use the WSOP for your standard you will find that you will be moving players almost for no purpose and will run yourself ragged moving players that probably don't need to be moved.
Also consider the staffing ability that we have compared to others. It's a lot easier to manage 108 players balancing within 1 with 2+ staff members then it is if you're by yourself. 12 tables is not a lot of ground to cover, but it is a problem when your in the money and play is fast and players are busting fairly frequently. That doesn't leave much time if your trying to payout players, balance tables and break tables at the same time.
So 12 tables is not for everyone.
Also this used to be when we usually go to 9 handed play. We generally don't always have the space. Nowadays we can go 9 handed on day 2's most of the time.