You can use the four π as the bass bin with seven π midhorn, tweeter and crossover. No changes are necessary in most cases. Naturally, since the design expects corner loading for the woofer, if used in free space, the bass will be weak. But the midhorn isn't optimal in free-space either. So the best placement is still in or near the corner, or at least back against a wall. The midhorn should be set right on top of the bass bin, to keep them close together. It is best to keep them less than a foot apart.