If I were to describe the words left, right, front and back, I could say, those are positions.
But what if I need to divide those into smaller groups: left and right, front and back?
How could I describe those smaller groups?
It depends in part what you're describing and if there is already a pattern established for such positions, for example, in anatomy, anteromedial combines front and center.
But assuming there is no pattern, I would use the usual adjective suggestions: use the main adjective and modify it with the other.
On a written page, we usually describe something's placement as in the "upper left corner" rather than "left upper corner". For a crowded room, I would use front left, rear left, front right, rear right.
On the other hand, describing pockets, the side usually comes first: left front pocket, right front pocket, etc.
So, the context of what position you're trying to refer to matters.
Your smaller groupings are in opposite directions along an axis.
"Up" and "down" would also be considered to be polar opposite directions in the same way.
In a Cartesian coordinate system, these would be along the x-, y-, and z-axis.