Like the others said, it’s complicated and that’s what the logs are for.
I’m commenting mostly as a shameless plug for this thing I made:
It’s for MRP not PO suggestions but they are very similar, so you might reconfigure it to work for PO suggestions
And also to say that you might also add your vote to Tim’s idea (that’s what that post is actually about), and/or Mark’s idea (in the replies), since they seem to encompass your concerns also.