Nerik
Assessing whether you are on a collision course with another aircraft is remarkably simple. The other aircraft will not move in your transparency. It just grows bigger. This applies regardless of the aspect.
So, if you look (say) 85 deg left and happen to see another aircraft at about your height and on a similar heading, place a chinagraph spot over the other aircraft and if it stays behind the spot you made you WILL hit it in due course unless one of you changes something.
This is a very useful thing to appreciate.
It is also why some guys make better fighter pilots than others - they find it easier to set up such a situation deliberately.