The wiki says that the Inserter capacity bonus technology is not effect for the Non-Stack Inserter's catching from machine/chest to belt or belt to machine/chest, it's only 1 bonu at the past version(0.12.x).Therefore, the bonus typically only applies when moving from machine/chest to machine/chest, and not from machine/chest to belt or belt to machine/chest.
Now I found that the capacity of Non-Stack Inserter's catching are be effected by this technology and is increase with the upgrade of the technology.
I know the new feature of Stack Inserter, but the key word is Non-Stack Inserter and from machine/chest to belt or belt to machine/chest. If the Non-Stack Inserter's capacity is increase where 's catching from belt to chest or inverse, why I does not use the Stack Inserter.