diff --git a/engine/turn.go b/engine/turn.go
index 6d02cdb..ccc50fc 100644
--- a/engine/turn.go
+++ b/engine/turn.go
@@ -128,31 +128,8 @@ func (gs *GameState) executeZone() {
 		gs.updateZoneRadiusToContainBots()
 	}
 
-	// Update zone center to midpoint of living bots (forces bots together)
-	// This is the key forcing function: zone shrinks around where bots actually are,
-	// not a fixed map center. Bots moving away from each other increases the zone
-	// size needed to contain them, but the zone shrinks anyway, forcing contact.
-	if gs.ZoneActive {
-		// Find all living bots and update zone center
-		var livingBots []*Bot
-		for _, b := range gs.Bots {
-			if b.Alive {
-				livingBots = append(livingBots, b)
-			}
-		}
-
-		if len(livingBots) > 0 {
-			var sumRow, sumCol int
-			for _, b := range livingBots {
-				sumRow += b.Position.Row
-				sumCol += b.Position.Col
-			}
-			gs.ZoneCenter = Position{
-				Row: sumRow / len(livingBots),
-				Col: sumCol / len(livingBots),
-			}
-		}
-	}
+	// Zone center is fixed at map center (set in NewGameState)
+	// This forces bots toward the center as the zone shrinks, ensuring contact.
 
 	// Check if zone should shrink (skip the turn zone starts)
 	if gs.ZoneActive && !zoneJustStarted && (gs.Turn-gs.Config.ZoneStartTurn)%gs.Config.ZoneShrinkInterval == 0 {
@@ -162,6 +139,10 @@ func (gs *GameState) executeZone() {
 				gs.ZoneRadius = gs.Config.ZoneMinRadius
 			}
 		}
+		// Ensure zone radius is at least the minimum (handles overshoot from shrink step)
+		if gs.ZoneRadius < gs.Config.ZoneMinRadius {
+			gs.ZoneRadius = gs.Config.ZoneMinRadius
+		}
 	}
 
 	// Kill bots outside the zone (only when zone is active)
diff --git a/engine/types.go b/engine/types.go
index 86c8598..b6cc315 100644
--- a/engine/types.go
+++ b/engine/types.go
@@ -240,10 +240,10 @@ func ConfigForPlayers(numPlayers, coresPerPlayer int) Config {
 	// Zone diameter must be <= 2 * attack radius so bots at opposite zone edges can reach each other
 	// Target: 65-80% combat density per plan §3.7.1
 	if numPlayers == 2 {
-		cfg.ZoneStartTurn = 5      // Start earlier to force combat before bots can spread
+		cfg.ZoneStartTurn = 10     // Per plan §3.7.1 to force combat before bots can spread
 		cfg.ZoneShrinkInterval = 1 // Per plan §3.7.1
-		cfg.ZoneShrinkStep = 6     // Shrink faster to force combat quickly (20->8 in 2 turns)
-		cfg.ZoneMinRadius = 0      // Force bots to same tile - guaranteed combat
+		cfg.ZoneShrinkStep = 2     // Per plan §3.7.1: 2 tiles per step forces engagement
+		cfg.ZoneMinRadius = 2      // Per plan §3.7.1: 2-player min radius
 		cfg.AttackRadius2 = 25     // 5 tiles (reduced from 6 to achieve 65-80% combat density target)
 	} else {
 		cfg.ZoneStartTurn = 10     // Per plan §3.7.1