The constant factor leads to the constant increase from point-to-point. Reducing the constant factor will make less increase from point-to-point and, thus making the curve shallower.
Work Step by Step
To figure this out, notice that each point shown in Fig. 1.8 is 3x greater (y value) than the previous point. Use an imaginary lower constant factor: 2x. The data points would then be 2, 4, 8, 16, which is a shallower curve. You could graph this yourself if the point is not obvious in your imagination.