Lucian's Ultimate only deals 100% damage to minions currently instead of 400%

Just like the title says, I was playing Lucian and I noticed that The Culling only killed like 3 melee minions with a total of around 1600 physical damage. On the tooltip of The Culling it was showing that my ultimate should deal 1693 physical damage in total, which fits with the health of those 3 minions...However it is supposed to deal 400% damage which is around 6800 and clear the whole minion wave instantly.