There was plenty of time to turn or change level as I had given plenty of warning of the unknown traffic, but the pilot seemed intent on getting as close to it as possible.
It may be obvious to
you which way to turn to increase separation, but it's not necessarily obvious to the pilot. "12 o'clock" is a 30 degree wide sector, and a turn away may just make things worse. What's more helpful from a traffic point of view is knowing which side the target is likely to pass. That allows a manoeuvre to increase separation.