Venom: the portal is the whole thing, the outside is one layer that to a degree stabilizes the node, as well as providing a mount for the power systems and control station. Most importantly, it protects against sudden changes in subspace which may destabilize the node- since the whole thing still is prone to collapse, etc. The inner ring is more like the Knossos itself, with interlocking subspace generators further stabilizing the node and allowing access. It's effective enough that it's not impossible to jump outside the central ring, subspace warps just become less and less stable as one gets farther from the center, with the node nonexistent altogether outside the outer ring. The little quarter-ring also has a complex task in stabilizing the node, suffice it to say that using the node outside the radius of that is a VERY stupid thing to do.
