I am wondering how to define the mask margin area for NORM10sided mask?
There is a PDF file posted by EETKorea, which explains how to use FlexDCA and the mask margin feature. You only need a compatible PDF reader installed (eg. Adobe Reader) to open the file.
Download PDF: http://www.eetkorea.com/STATIC/PDF/201208/EEKOL_2012AUG07_OPT_TEST_AN_01.pdf?SOURCES=DOWNLOAD
Note: Use "mask" as search to find the information faster.