Ion Shield with 2 points added in to it will add 2% damage reduction to your already 5% damage reduction from Ion Cell. So with that in mind you will have a 7% damage reduction on a mob if you put 2 points in to Ion shield. So a boss hits you for 150,000 over a 10 min fight with the 2 point in Ion shield you will reduce the damage by 10,500 *That is a 7% reduction* with out the 2 points you will reduce the damage taken by only 7,500.