Impact of Event class selecting Input Source while creating mapping set

Content

I am trying to create a mapping set based on the project organization cost center segment for procurement charge account. When i search Project Organization Cost Center Segment I find too many source as project organization cost center segment with few blank event class and few with different event class such as Labor Cost, Revenue etc.

 

But i am not sure what source (Project Organization Cost Center Segment ) to select with event class, when i select the source with event class as miscellaneous the charge account is not working.

 

Could you please advice how do i achieve this.