Reduce atmospheric shielding multiplier

- With "proper" atmospheric density definitions for gas giants, there is less variance in most body's atmospheric density.
- Heavy atmospheric shielding on an AC33 still supports a maximum static pressure exceeding that of real-world nuclear submarines

data/libs/Equipment.lua

@@ -65,13 +65,13 @@ misc.missile_naval = EquipType.New({
 })
 misc.atmospheric_shielding = EquipType.New({
 	l10n_key="ATMOSPHERIC_SHIELDING", slots="atmo_shield", price=200,
-	capabilities={mass=1, atmo_shield=9},
+	capabilities={mass=1, atmo_shield=4},
 	purchasable=true, tech_level=3,
 	icon_name="equip_atmo_shield_generator"
 })
 misc.heavy_atmospheric_shielding = EquipType.New({
 	l10n_key="ATMOSPHERIC_SHIELDING_HEAVY", slots="atmo_shield", price=900,
-	capabilities={mass=2, atmo_shield=19},
+	capabilities={mass=2, atmo_shield=9},
 	purchasable=true, tech_level=5,
 	icon_name="equip_atmo_shield_generator"
 })