When it comes to feedback, ensure that you give the engineer recieving the feedback the maximum potential to grow to ensure the engineer does a better job next time.
1: Engineer is junior in the context and insecure/unmotivated: Do X
2: Engineer is junior in the context and motivated/secure: Take the decision for the engineer and explain why
3: Engineer is senior in the context but insecure: Coach by open ended questions: how large of a function do you think is appropriate?
4: Engineer is senior and motivated/secure: From your perspective how should the function be and how should we do this in the future to reach our goals.