I like it the way it is, but yea if there is any lag (particularly ps3 graphical lagging) I've had some minor problems because even though the animation is lagging, the IB just keeps ticking, by the time the big hit is displayed IB has fallen off. Doesn't always happen but the times I've noticed it are for Titan's MB and Ultima's Diffractive Laser.

Seems like it's short duration is to balance uptime with other CDs. As Nate mentioned, at 12 secs you could have it up 60% of the time, though it's being slightly balanced by decreased potency. I personally prefer the higher mitigation/shorter duration, 30% uptime seems to be about the norm for buffs.