Ptime for g729 does not increases past 120ms

In Asterisk Documentation the maximum ptime for g729 is given 230ms: … ketization
But in my case (Asterisk 1.8 on Centos 5.6) ptime is not increasing past 120 ms no matter what i put in conf.
I have opened a issue regarding this in Asterisk issue tracker:

The G.729 codec is a Digium commercial product and not supported here or on the open source bug tracker. You should report problems through the commercial support channels, not the open source ones.

Why do you want a round trip time which would not have been permitted on the PSTN, even when satellite links were common?