I agree that helping the largest number of people in need on a particular issue is important.  I think we also need to consider both the resources we have available to us and the area of geography that we are needing to align with.   Our Foundation is restricted to a specific geography based on government direction and historical relationships.  Within this geography there may be more need is certain areas than others, but either there are others that are helping to meet this need in that area while there are few helping to meet this need in a area of lower population.   So we look to fill gaps where we think we can have an impact even if the numbers helped are lower.  

Our organization has been exploring how to do more effective altruism by focusing more geographically and population-specific.   This requiring us to say No to those we have said Yes to before.  We need to find better ways to communicate this so that those we are saying No to understand our logic and those we are saying Yes to understand the impact we hope can be achieved by working together.