"twice as much" vs. "twice as much again"

Hello,

Could you please suggest whether both following expressions

have the same meaning

(i) twice as much as (200%)

(ii) twice as much again as (200%?)

? My dictionary says that they both refer to 200%. However, the

following expressions make me impugn the translation of (ii)
provided by the dictionary:

(iii) half as much (50%)

(iv) half as much again (150%)

According to (iv), (ii) should mean 300%. Am I wrong?

Thanks in advance.

--

Victor