Logic is to increase the number of immigrants from cultures and regions where people are fitting in well and succeeding. Eg.. Chinese immigrants do well everywhere I have read about. Lower crime rate, higher income, higher education attainment level then the host population.
On the other hand it is only logical to decrease the numbers from cultures and regions where those immigrants are not fitting in well. Eg.. Higher violent crime, organized crime or worse terrorism, low income, heavy use of government services, while paying low amounts of taxation, etc..
If some hug the world, marxist leftists gets in and has a big theory about how ‘this time its different’, they now know how to integrate a cultural group that didn’t fit in before. Don’t jump head over heels in, first invite a few thousand, then study how they fit in over say 20 years. Using your ‘different’ techniques. If it works then increase it gradually after the 20 years.
From my experience and observations, Africans tend to fit in fairly well.