When I pass other cyclists on the road while commuting I give them many feet of clearance.* Most often this means passing using adjacent lane or the left track of same lane. I won't pass if it means squeezing between a motor vehicle and them, so in this case I wait for a gap and then as there is a gap I can use the full lane width.

I wouldn't ever be surprised by another cyclist passing me as I use a mirror. If they passed with 6" clearance and they could have easily been further away thats a bit rude and unneccessary. If they didn't have much more room, again I'd see it coming and not be surprised.

Actually on my commute I have never once been passed by another cyclist. All this means is that faster cyclists don't use the same route at the same time I do.

*The one exception to this is cyclists I 'know'

Al