I'm using RTD only for getting position info. The syntax is:
=RTD("Position.Server", , "SBUX", "E", "xxxx", "nPos")
=RTD("Position.Server", , "SBUX", "E", "xxx", "fPosAvgPrc")
The first one is the size and the second is the avg price. "xxxx" is the last 4 digits of your account...