The definition of Lookalike Audiences in Facebook is:
x% of Facebook users in the selected area that are most similar to the users in the base audience.
Based on this, the "1%-Lookalike Audience" for the US, for example, will always have approximately 2 Million users, because there are approximately 200 Million Facebook users in the US. The "2%-LAA" will have approximately 4 Million users, and these 4 Million INCLUDE ALL of the 2 Million users in the 1%-LAA.
No LAA will include ANY of the users that are in the base audience, by the way!
Lookalike Audiences will automatically update when the base audience improves. If the base audience shrinks, the LAAs that are built with it will NOT update.
Facebook also supports what I like to call "Interval LAAs'. They are named, for example 1-2%, 1-3%, 3-5% etc.
These Interval LAAs automatically EXCLUDE the LAA of the first value from the LAA of the second value. So, 1-2% LAA is actually 2%-LAA MINUS 1%-LAA, and the US version of that has approximately 2 Million users.
Since you can also exclude audiences when you set up the audience for an ad set, I find it better for LAA manegement to exclude LAA's there, rather than using the Interval LAAs. In other words, I will just build the 1%-LAA and 2%-LAA, and if I want to target the same audience as with Facebook's 1-2% LAA, I INLCUDE the 2%-LAA and EXCLUDE the 1%-LAA in the ad set audience.
This allows me to be completely flexible in my targeting. For example, I can target the same audience as with "2-6% LAA" by INCLUDING 6%-LAA and EXCLUDING 2%-LAA, and I only need to create an manage the simple LAAs (which are a big enough hassle to deal with...)
We don't support "interval" LAAs in Trackify because we think they're pretty useless and just make for a lot of clutter in your Audience Manager.
You can accomplish all you can do with the interval LAAs by just creating all simple LAAs, and then excluding whichever segment you don't want to target in your ad sets when you set up the audiences there.
For the 3-6% LAA for example, you would just INCLUDE the 6% audience and EXCLUDE the 3% and that's the same as the interval.
Since you would need to create A LOT of interval audiences to cover all possible combinations, it's far more flexible to work with the simple LAAs and the exclusion option.
By the way: Did you know that you can create Lookalike Audiences for up to 20% in Trackify? And you can create them in bulk, saving you a ton of time versus just using the Facebook Audience manager.