Actually I did find a solution to this.
<local-directory path="xxx">entry explainedas follows :
<!-- The optional path attribute gives the prefix of the sar entries that should be copied into the data directory. If it is not specified the entire sar contents will be placed into the data directory. -->
This actually put my txt files into server/$config/data folder. The only question remaining is that is it the right way to resolve this issue ?
Is it the right usage of the <local-directory> element ?