I don't know what you meant. You asked if I know what a zone is, implying that the rules for zones have any relevance whatsoever to determining the rules for Wall of Fire. They don't.
So I have no idea where you were going with that.
Where the space within a wall of fire deals damage upon entering it.
The space doesn't deal the damage. The Wall of Fire deals the damage.
It's not the terrain that damages the creature, it's the conjuration occupying that terrain.
Actually it is a very small mobile zone that happens to follow the zone rules except where the specifics of the power and the differences between the zone and conjuration are applied.
It doesn't follow any of the zone rules. We could excise the zone rules entirely from the PHB with absolutely zero effect on the functioning of Flaming Sphere, because it doesn't reference them, they don't apply to it, and they're entirely irrelevant.
I can remove every reference to "Close Attack" from the rules, and it won't alter the behaviour of my basic melee attack one bit. So for evaluation of how a basic melee attack works, any discussion of Close Attacks is irrelevant. It's incorrect to say "A basic melee attack is a Close Burst 1; Target: 1 creature in burst; Special: If you cannot see the target, you must choose a square", etc... because it's
not a Close attack. It's especially incorrect if you then use this invalid 'comparison' to then start applying Close-specific rules to your basic melee attack.
I can remove every reference to "Zone" from the rules, and it won't alter the behaviour of Wall of Fire one bit. So for evaluation of how Wall of Fire works, any discussion of Zones is irrelevant. It's incorrect to call a Wall of Fire a Zone-with-a-few-special-rules; it's especially incorrect if you then start referencing Zone-specific rules and deciding they apply.
-Hyp.