This was discussed briefly in another thread and it would appear it's just the way it is. I would assume that it's a first pass radiator so is the hottest and therefore the one that steams. Mine does it every time it's cold just from the driver side and I'm just used to it.
My21 started doing it about 6 months ago, does it after switching engine off on drivers side (commuting about 10 miles to and from work), initially thought it maybe a bit of a weep/leak from coolant or screen wash dropping onto something hot.
I've noticed the steam drifting up over the bonnet when I pull up at a set of traffic lights or whatever so it definitely does it with the engine still running, it could still be what you've said though. I don't really care about it that much, I've grown to think it looks kinda cool steaming when you pull up somewhere. Like the DeLorean having just done a time jump.
