Put portal B facing north, portal A facing west, and jump into A facing west, and you'll come out of B facing south. If you start putting portals on the ground in other directions, everything stays logical. So far so good, and consistent with the way portals work. You need to know this for several advanced chambers and challenges, when you jump into one and come out of the other, and have to move backwards to get onto a platform. When you jump into one portal, still facing north and looking down, you will come out of the other portal, looking up and now facing south. You put 2 portals on the ground, next to each other.
Picture the following situation: you're standing somewhere, facing north. Something physical to represent both 2 portals and yourself could be useful. Something about test chamber 18 has been bothering me for a while.