You are thinking of the original set up - For four, I went with the layout as preferred by Floyd Toole - side wall placement.

The only subwoofer facing into the room is the Horizontal. Of course, when you consider the shortest wavelengths these guys handle are about 7 feet in length (for the 80 Hz signal), forward or rear facing is not much of an issue.

Surprisingly, as detailed by Dr. Toole, phasing in this position is rather simple.