As too close for comfort seems to have vanished up it's own backside, I will re-ignite here
Consider for example the type and frequensy of scan you use, are you focussing on the GPS? or anything else in or out of the cockpit, ideally, your head should never stop moving.
Agreed 100% I would add that you will also need to manouvre the aircraft to clear blind spots. For example dipping the right wing to see under the left wing before a left turn (high wing a/c)
I am in the happy position of having a rear view mirror on the strut, intended to use in watching the glider when I am towing, but pretty useful in general lookout.
Specially as practically everyone flys faster than me
Saints preserve us from those

who rely on the radio to do their lookout for them