Throughput is very low

[Mamun Abu-Tair]

Dear all, 
I am trying to do throughput test with copmex AC cards Model (WLE900VX 7AA) .,using hostapd running on the server and  one client. 

I used Kalle sitting for the hostapd. However, the maximum throughput i can get is around 70Mbit/s which is far away from the throughput achieved by many users (UDP traffic). 

I have notice that Bit Rate keeps fixed 6 Mb/s . and it dose not responding to any commands to change it. 

The machines used: 
 Ubuntu 12.04, Kerenl 3.16 , updated regulatory to cover 80Mhz channels , and the latest  firmware 

Your help is appreciated . 
Kind regards 
Mamun