Make miasma start being visible later (#10128)

Content.Shared/Atmos/Prototypes/GasPrototype.cs

@@ -44,7 +44,10 @@ namespace Content.Shared.Atmos.Prototypes
         /// <summary>
         ///     Visibility for this gas will be max after this value.
         /// </summary>
-        public float GasMolesVisibleMax => GasMolesVisible * Atmospherics.FactorGasVisibleMax;
+        public float GasMolesVisibleMax => GasMolesVisible * GasVisibilityFactor;
+
+        [DataField("gasVisbilityFactor")]
+        public float GasVisibilityFactor = Atmospherics.FactorGasVisibleMax;
 
         /// <summary>
         ///     If this reagent is in gas form, this is the path to the overlay that will be used to make the gas visible.