The addition of large fibers or particles to a matrix of fine particles is known to increase the packing density of a bimodally-distributed powder compact. When the addition is more than 100 times larger than the matrix fine particles, the ideal packing density is well described by Furnas' relationships. When the size difference is limited, the extra pore volume created is non-negligible and lowers the packing density from the ideal packing density. A model accounting for the effect of extra pore volume on pacing density in bimodal and trimodal systems has been successfully developed. The model is extended in this paper to predict theoretically the packing density of a fine particle matrix with mid-sized particles and large aligned fibers. For sizes 25 or 100 times larger than the fine particles, the addition of a mid-sized population to a fine particle/fiber compact generally gives a large increase in compact density. Skewing the mid-sized particles to a larger size generally decreases the extra pore volume and increases the overall packing density. However, over-skewing can lead to a degradation in the packing of a mid-sized particles and a decrease in relative compact density. In the case of fibers 25 times larger than the fine particles, the optimal packing density can be achieved by adding mid-sized particles ten times larger than the fine particles.