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These tutorials are exactly what I was looking for. I pretty much get it now. The key take-away is this graph, which explains what the shape of the curve means:

• The vertical height of the curve determines the intensity of the layer style. The very bottom means that the layer style will be transparent; the very top means that the layer style will be at full intensity.
• The horizontal positioning of the curve determines where the layer style appears on your shape: toward the left means that the layer style will affect the center interior of your shape. Towards the right means that the layer style will affect the shape out near its edges. 

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For anybody else interested in experimenting with this, it's best to work big (try very large, chunky text) to really see what's happening. It's also best to start with Inner Glow, which is the easiest to see exactly what's going on with the different contour effects. My mistake in the past is that I was applying contours to the Bevel & Emboss layer style. You can do it, but it's much less intuitive to understanding gloss contours because the B&E layer style has an additional component—the light direction—which can greatly confuse the issue.