Mant19 sector with RB921

Hello all friends
I need to know what’s the maximum number of wireless stations that the Mant19 sector can handle on the 3 protocols
NV2, Nstream and 802.11
I’m facing a problem that is when I exceed 12 clients connected to the sector, all clients will have disconnections on ping, clients are. Mixed of LHG5 and LDF5, total bandwidth for all clients is less that 50mbps, Mant19 is set to AP-bridge no routings.
Any help

http://forum.mikrotik.com/t/mant19-sector-with-rb921/128092/1