The description for Wall of Fire states:
You can make the wall up to 60 feet long, 20 feet high, and 1 foot thick, or a ringed wall up to 20 feet in diameter, 20 feet high, and 1 foot thick.
One side of the wall, selected by you when you cast this spell, deals 5d8 fire damage to each creature that ends its turn within 10 feet of that side or inside the wall. A creature takes the same damage when it enters the wall for the first time on a turn or ends its turn there. The other side of the wall deals no damage.
A caster wants to create a Wall of Fire, but they are in a tight space, say a 10′ x 10′ room, with the target in the center and all the other party members are against different walls. Since the spells says the diameter can be up to 20 feet, they decide to create a tighter circle, say 8 foot diameter leaving a little bit of space between the outside of the fire wall and the walls of the room with the hot side pointing inward.
But the spell has two parameters for where things would take damage; inside the wall or within 10 feet of the hot side.
Does the fire from one side of the circle extend outward past the opposite side of the circle to damage creatures?
In other words, the northern-most point of the circle has the heat extend out 10 feet. Does this heat/damage pass through the southern-most point of the circle or does the cool side stay cool?