In most cases , the use of look a like is created from a custom audience , and with it the lookalike generated will have more relevance.
researching the api facebook ads, found this:
When optimized for similarity, a lookalike audience will include the top 1% of people in the selected country who are most similar to the seed Custom Audience. The reach of the new audience will be smaller, but the match will be more precise.
When optimized for reach, a lookalike audience will include the top 5% of people in the selected country that are similar to the seed Custom Audience, but with a less precise match.
Instead of using types you can manually set a ratio value that represents the top x% of the audience in the selected country. The ratio value should be between 1%-20% and should be specified in intervals of 1%.