Imp Shadow Word: Does more DMG or spreads DMG longer?

[artifact23]

Shadow Word: Pain (At my level)
"A word of darkness that causes 234 shadow damage over 18 seconds"

Improved Shadow Word Pain
"Increases the duration of your Shadow Word: Pain spell by (3/6) seconds"


So in other words it does the exact same amount of damage, it only increases the duration of the spell. So instead of doing 234 shadow damage over 18 seconds, it does 234 shadow damage over 21/24 seconds. So without Improved SWP I'm doing 13 damage per second with the spell for 18 seconds (234 / 18 = 13). WITH Improved SWP I'm doing 9.75 DPS with Improved SWP (234 / 24 = 9.75). What am I misunderstanding? Why on earth would anyone want this?

Unless the articulation is crooked. I've always wondered this, and never put points here because of it.

[NikeTheSword]

It adds two more ticks to the dot (one for each 3sec upgrade), thus increasing overall dmg.

[artifact23]

Thanks.