Offsetting from SIDs / STARs
It is my understanding that to ensure separation from terrain and other routes, you must adhere to SID / STAR routes within the tolerances of whichever RNP you are operating under, unless cleared for the deviation due to weather.
However today (like many other times here in China) ATC instructed me to offset 2 miles right just as I was about to start the STAR. One airport we frequent always tells us to offset 15 miles left for the STAR. In both cases the SID is the same route as the STAR and by offsetting they essentially get a two way street.
So - is this legal? How accurately do we really have to fly SIDs / STARs?