My instructor always told me to look for an object in the sky that does
not appear to be moving. If you see that, do something immediately,
because you are dead-on a collision course.

I've had what I consider close calls over the years, the most memorable
being when I saw an SR-22 dart across my field of view from right to
left very quickly. I immediately banked over to the right at a 45
degree angle and pulled hard to insure we'd pass behind the guy - he
appeared to do absolutely nothing.

Basically my theory is that mid-airs can only happen when both pilots
are inattentive, or neither can see the other due to a perfect
alignment obscuring both planes behind wings, struts, or what have you.
Since you seem to be overly cautious, I'd suggest that you have nothing
to worry about... but don't stop being as vigilant as you are - that's
exactly how I think one should approach flying... always be thinking
ahead of the plane, and that includes keeping up your visual see &
avoid scan.

--
Guy