Seems backspacing confuses a lot of people, which makes sense since it's a stupid way to measure offset (the method, not the concept). Here's a place that gives a good chart. The gist of it is that the backspacing measurement is the distance from the back of the wheel to the centerline plus...
How long is your commute? I could see shorter commutes resulting in a lot of water from blow-by condensing in the can. Burning gas does create a lot of water, so blow-by gasses would naturally have a fairly high water content. My theory would be that the water vapour wouldn't condense once...