I must be doing something wrong... Wiki has the equation as:

Roundtime = Weapon Speed + ((Number of Strikes - 1) * (Weapon Speed / 2)) + 1

Then I assume there's a straight deduction from agidex. But with my claidhmore (base 8) and 3 agidex...

2 strikes = 8 + ((2-1)*(8/2))+1 = 8+(4)+1 = 13 - 3 agidex = 10 seconds (which is correct)
3 strikes = 8 + ((3-1)*(8/2))+1 = 8+(8)+1 = 17 - 3 agidex = 14 seconds (this is incorrect, my swing time is 12 seconds)

I use no enhancives. Anyone see where the issue is?