Going back and actually reading ALL of his words, I found that this is what he said:
A good tuned exhaust will typically increase VE and torque by 15-20%, over the open-exhaust numbers and by about 25-30% over a regular silencer (RPM by 10-15% higher).
I may be wrong, as my knowledge of English is rather elementary, but he is saying that tuned exhausts give a bigger improvement over the regular silencer (25-30%) than with the open exhaust (15-20%). That is, he is saying that open exhaust has better VE and torque compared to a regular silencer.
Have I used all the words & do my posts make sense? Never mind if they dont. Cause this discussion is serving no purpose other than to marshall more and more opinion against me, the poor newbie who is supposed to ask questions like "D-Uh, I got an OS and I dont know the glow plug from the backplate", as opposed to talking about gas flow and Doppler anemometry.