The RTP's viewpoint only shows walls facing down. Look at one of the cave tilesets to see my point.
The walls facing down are visible, the left and right aren't, and the up ones are passable because they block the player's view of the ground.
Your walls are visible from both the left and right, and based off the corners the up ones aren't passable.
The walls facing down are visible, the left and right aren't, and the up ones are passable because they block the player's view of the ground.
Your walls are visible from both the left and right, and based off the corners the up ones aren't passable.