It probably depends on what carrier is sending the package and if they price shipping based on weight, on dimensions, or some combination of the two.
While figures tend to occupy more space, they generally aren't very heavy. Out of curiosity, I compared the weight of two figures I had boxed-up (one was a 1/5 scale and the other was a 1/6 scale figure) and 4 FAKKU books and there actually wasn't that much difference in weight. In fact, the books were slightly heavier than the figures.