DesignDawg:
Tripleshot and
Windogg are correct (all "advocacy" aside -

) . . .
Eye contact is irrelevent - If you can't see my mirrors from behind, I can't see
your car, much less you!
You've also cut your reaction time to any maneuvers I may initiate to less than a second; And you will have absolutely no warning whatsoever about potential road hazards like potholes or tire carcasses in your path. "Craters and Gators" don't affect me all that much, but imagine what 40 lbs of scrap tire tread (kicked up by my tires) would do to your windshield at 60+ MPH . . .
Windogg is also correct in asserting that you shouldn't remain alongside my rig for extended periods.
If you're passing, then execute the pass, allow a few car lengths distance, and return to the travel lane. Remember that I'm attempting to maintain adequate stopping distance with the vehicle(s) ahead of me - Don't just cut in as soon as you clear my front bumper.
Don't pass on the right. I'll be appearing in court in a couple of weeks thanks to a moron that decided to "get around me" on the right side after following me while I legally passed some vehicles. It never occured to him that I might return to the right lane, and he never saw my signal. He panicked, lost control, hit my tractor and ended up in the median; but since he had a passenger for a "witness", I got the ticket for "Unsafe Passing".
Although a loaded rig takes a substantial distance to stop, a partially loaded semi can be far more unpredictable. I may be able to slow down much faster than you expect; or the trailer brakes may lock up, causing the trailer to skid towards an adjacent lane. Either way, with a van-type trailer, you can't tell how it's loaded. Tank trailers are also unpredictable, since that liquid load is always moving.
In addition to
Tripleshot's valid point about greater visibility from our cab height, we also, by nature of experience, are generally better at assessing traffic patterns and predicting potential behavior or problems well before most car and light truck drivers. Unfortunately, most drivers only "look ahead" as far as the rear of the car in front of them, and depend on their reactions to avoid hazards or respond to various situations as they occur.
While I'm on the soapbox, I might as well add this:
Keep in mind that, when I activate my turn signals, I'm not
asking your permission to make a lane change; I'm
telling you where I need to go. Since we can't stop quickly at highway speeds, our greatest assets are observation, experience, prediction, and maneuvering.
In the extreme, my signals mean "Get out of the way, I need to be there"; They're not an invitation to a pissing contest over your "rights" to a few square meters of asphalt, or a message to "Speed up and pass so your not stuck behind the truck".
Don't misunderstand me - I'm not trying to project an attitude here. The important point is that peoples lives, possibly your own, depend on how you respond.