I think this is a fascinating question, as we want to optimize for autonomy and impact while making sure we create meaningful management - a sustainable structure where X IC + 1 M > X+1 IC. I tend to believe that a manager should have at least 5 reports (and up 8 or so), as it creates enough room to build an independent team around a problem domain, formed with different expertise (puzzle vs. replacements), working to solve a solution from A to Z. Great read from Daniel Pupius that would make you think about your organizational structure.