Well I finally got a mirror that lets me monitor the rear constantly. (Although I still need a better one as this one jiggles to much and shifts out of position over time)
But what I learned troubles me. On the PM commute I have a ~3mi of mulitlane (two and three lanes of same direction) densely traveled relatively high speed roads with only NOLs.
In these places I ride well into the lane to prevent cars from squeezing by me to close. I frequently get agressive and angry drivers as they have to slow and merge into next lane over, but with little gaps for them to do so. Yesterday I was honked at 4 separate times, one time was about 8 honks over a period of time.
What I observed it that some drivers get 'stuck' behind me for much longer that I thought. On this 3mi stretch one driver was behind me for a good 1/2mi and was angry after about 1/4mi honking and swerving left to right real close to me. They simply could not pass me as traffic in the adjacent lane was 45mph+, but we were traveling 20-25mph. When they finally did the 2nd car behind them tried also (accerated hard) and couldn't make the gap and braked hard at last minute with tire squeal (which I had previously heard on occasion, but not known why)
I actually felt a bit concerned holding up cars like this and putting them in a situation where they need to agressively pass to get around me. I know why they are stressed, not (just) because they are slowed by me, but because the merge to pass me is not an easy manever in such traffic.
Anyway there was a lot more 'action' going on behind me that I was aware of as previously I only made the occasional shoulder check.
I'll see how it goes today, maybe yesterday was just worse than usual.