In case you haven't noticed yet (and not everyone does), the FD shifter's trim click should be able to avoid rubbing the chain when cross-chaining.

One rub that may happen in the small-small combo on some bikes, even though your bike may not be experiencing it, would be when the chain rubs against parts on the inboard surface of the big chainring. I've noticed it more on some cranksets than others, and only in a compact style. The bigger size difference between the chainrings (50-34 versus a standard double's 53-39, for example) makes it happen.