Face to the growing demand of multimedia services, over wireless local area networks, ensuring an efficient and reliable multicast transmission becomes a necessity. Thus, the upcoming 802.11aa amendment has proposed the group addressed transmission service (GATS) to overcome problems caused by the absence of feedback in multicast transmission. We focus in this paper on the group cast with retries block Ack policy. Thus, we perform an analytic study to investigate the impact of the selection of recipients asked for acknowledgement on the network performance. Further, we propose a scheme to select the appropriate recipients asked for acknowledgement when the group addressed members show different channel conditions.