Helmet Head

I beg to differ... Unless you consider San Diego to not be a decent sized city?

There are two basic lane positioning methods:

1. Keep to the right unless unsafe or impractical to do so (using your words). The primary riding position is "as close as practicable to the right". The secondary position is more centerish.
2. Keep centerish except to allow faster traffic to pass when safe and reasonable to do so. The primary riding position is centerish. The secondary position is about 3 feet to the outside of passing traffic.

Of course, often times, the cyclist riding according to A is going to choose the same position as the cyclist riding according to B. But the problem with adopting A is that you are more likely to end up being in an inconspicious position unnecessarily at a critical moment.

One way to think of the difference between A and B is having a mental spring that tends to pull you into your primary/default position. Thus, the A cyclist is constantly being pulled to the side, and he has to make a conscious effort to note that conditions are such that he should be in a more centerish position temporarily. The B cyclist is opposite: for him, the centerish position is the default, and he actually has to "work" to pull aside temporarily.

To the A cyclist, because his default position is off to the side, it's easy to not notice all the long gaps that occur in traffic. They're irrelevant or insignificant, so they're missed. He ends up believing, "The exceptions are so few it hardly makes a difference to get back into the center of the lane". In these words you can almost feel the effort the A cyclist wishes to avoid in working against the A spring that keeps him at the side most of the time.

Upgrade your A spring to a B spring. Vive la difference!