Hi
Thanks for sharing the resolution of your issue.
For understanding group condition and its functionality please check SAP Note Note 24944 - Group conditions and following link.
http://www.saptechies.org/faq-header-conditionsheader-condition-screen-876617/
I am not sure but I think for group condition system checks only material pricing group field MVKE-KONDM. If anyone of you have tested this or knows that which field is considered for a group condition, please share.
Thank$