I have seen on these forums that it is dangerous to go against Zuberi in a rules argument, but because I am still grumpy that my newly-summoned phalanx of goblin legionnaires was shredded by a wall of pikes + force wave combo last night, here goes.
A normal wall doesn't block line of sight to itself. I think we can all agree on that. Thus, it doesn't block line of sight TO the zone border that it occupies. It just blocks any attempts to trace line of sight ACROSS the zone border it occupies.
Agreed.
Similarly, a Steep Hill doesn't block line of sight TO the second border of the zone it sits in. It only blocks line of sight ACROSS the second border. Ergo, you can target a wall on the opposite side of a steep hill.
This is where we differ. Let me start off by reflecting your first paragraph to indicate what I think is going on, and then I'll try to explain why.
A Steep Hill doesn't block line of sight to itself. I think we can all agree on that. Thus, it doesn't block line of sight TO the zone that it occupies. It just blocks any attempts to trace line of sight ACROSS the zone it occupies.
The key is the language used on the Steep Hill card: "LoS which passes through two sides of this zone is blocked."
Various posts on this thread, including Zuberi's, have equated 'sides' here to mean 'zone borders'. I don't think it does. Arcane Wonders has been in this business for a long time, and I give them the benefit of the doubt when it comes to the language they use. If they meant 'side' to mean 'zone border', they would surely have written 'zone border.' They must have been thinking of a different concept with 'side'. (In passing, I note that the codex definition for Zone Border does not use the word 'side' anywhere.)
I would argue that the intent is to differentiate the Hill's effect from the rulebook's section on Line of Sight, which is explicitly and only discussing LoS as it relates to walls and zone borders, and is silent on LoS as it relates to conjurations inside a zone.
I'd like to see an official ruling, but before such a thing shows up, I present my theory:
The Steep Hill's wording introduces a second meaning for line of sight, one that is used in wargaming - a virtual line between the active creature and its target, where 'Zone borders' are not a relevant consideration but the 'sides' of the zone are.
With the Steep Hill what we have is some terrain that sits above the 'floor level' of the arena. Functionally it is like a building in a war game, one that effectively has the same ground dimensions as the zone it sits in. If you're standing in front of the 'SH building' you can only see and target its front wall and what is on its roof. if the line of sight passes through the 'SH building' you can't see through it to what is beyond, and you can't see or target its three far side walls (which would be the zone borders, so you couldn't build a wall on them).
A tidier way of putting it on the card might have been "LoS that passes beyond the centre of this zone is blocked."
As I say, that's my view. I appreciate that there are others and would love a ruling on it.