Open interest builds the walls, so it's natural to assume the strike with the most OI is the wall. Usually it's a good clue — but not always, because the force that pins price is gamma, and a strike's gamma depends on more than how many contracts sit there.
Why OI and gamma diverge
A strike's pinning power scales with its gamma, which is highest near the money and near expiration and fades for far or longer-dated strikes. So a huge-OI strike that's far from spot, or built from longer-dated contracts, can carry surprisingly little gamma — big number, weak wall. Meanwhile a more modest OI concentration right at the money can dominate the hedging. Raw OI counts contracts; it doesn't weight them by how much they actually move dealer hedging.
The biggest pile of contracts isn't automatically the biggest wall. Distance and expiry decide how much of that OI is actually gamma.
What actually makes a wall
The real wall is the strike with the largest gamma-weighted concentration — open interest multiplied by each strike's gamma, netted across the book. That's why a proper dealer map computes walls from the gamma profile, not from an open-interest leaderboard (see how to read dealer positioning).
The practical lesson
When you eyeball an options chain and spot a giant OI number, don't automatically trade it as a level — check whether it's near spot and near-dated enough to carry real gamma. A far-out OI mountain can be almost inert. NoVo draws the walls from the gamma-weighted picture for exactly this reason, so the level on your chart reflects hedging pressure, not just a headline contract count.