zstack broadcast star topology

I have a question: when I make up a zigbee network, it is a star topology.   1  Coordinator   and  60  EndDevices .   When the coordinator  broadcasts a message,why only 16 EndDevices can recieve the message?  Other 44 enddevices  can't recieve the broadcast message whenever.

Nobody meets the situation?  I think this is related to the configuration of  MAX_NEIGHBOR_ENTRIES  (nwk_globals.h)

when I change the MAX_NEIGHBOR_ENTRIES from 16 to 1,  15 more enddevices can recieve the broadcast message . But I don't know why?