diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index c879195..2938753 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -6344,6 +6344,28 @@ public sealed class GameWindow : IDisposable
             Lighting.Tick(camPos);
             var ubo = AcDream.Core.Lighting.SceneLightingUbo.Build(
                 Lighting, in atmo, camPos, (float)WorldTime.DayFraction);
+
+            // A.5 T22: override fog ramp with N₁/N₂-derived distances so the
+            // horizon fog masks the N₁ scenery boundary. Sky keyframe fog is
+            // retail-accurate at normal view distances but far too short for
+            // the extended N₂=12 (25×25 LB) streaming window.
+            // FogStart = N₁ × 192m × 0.7 ≈ 538m at defaults (4/12).
+            // FogEnd   = N₂ × 192m × 0.95 ≈ 2188m at defaults.
+            // Multipliers exposed as env vars for fast iteration at visual gate.
+            {
+                const float LandblockSize = 192.0f;
+                float startMult = ParseEnvFloat("ACDREAM_FOG_START_MULT", 0.7f);
+                float endMult   = ParseEnvFloat("ACDREAM_FOG_END_MULT",   0.95f);
+                float fogStart  = _nearRadius * LandblockSize * startMult;
+                float fogEnd    = _farRadius  * LandblockSize * endMult;
+                // Preserve fog color (xyz), lightning flash (z), and mode (w).
+                ubo.FogParams = new System.Numerics.Vector4(
+                    fogStart,
+                    fogEnd,
+                    ubo.FogParams.Z,   // lightning flash — unchanged
+                    ubo.FogParams.W);  // fog mode — unchanged
+            }
+
             _sceneLightingUbo?.Upload(ubo);
 
             // Never cull the landblock the player is currently on.
@@ -8862,6 +8884,17 @@ public sealed class GameWindow : IDisposable
         return copy[copy.Length - 1 - offset];
     }
 
+    /// <summary>A.5 T22: parse a float environment variable, returning
+    /// <paramref name="defaultValue"/> when the variable is absent or unparseable.</summary>
+    private static float ParseEnvFloat(string name, float defaultValue)
+    {
+        var s = System.Environment.GetEnvironmentVariable(name);
+        if (s is not null && float.TryParse(s, System.Globalization.NumberStyles.Float,
+                System.Globalization.CultureInfo.InvariantCulture, out var v))
+            return v;
+        return defaultValue;
+    }
+
     private void OnClosing()
     {
         // Phase A.1: join the streamer worker thread before tearing down GL