Quite a few near'ish (usually gliders) and 1 VERY near - maybe 2 spans away, passing at 90 degrees L-R, 28/Aug last year, N of Bournemouth, T tail (PA38?)
- in a few thousand hours.
I'm a believer in the "big sky small aeroplane" theory, lookout is important and helps but it cannot fully protect you.
One common failing with students when they see a close "bogey" - they don't turn towards so they can keep it in sight.
HFD