packet rate and Bandwidth speed

hi all
i have veri strange problem with my MK, i use 20Mbps wireles bridge to connect two MK routers, evrithing is OK until users using this link start to grow above 10. when this hapend my 20mbps wireless connection can’t do more then 11-12Mbps.
i test with “Bandwidth test” and on TCP can do more than 50kbps(interface to wireless bridge shows 11Mbps) when i try UDP i get 10-15Mbps (interface to wireless bridge shows 20-15Mbps)
ifond something confusing - “Torch” on interface to wireless bridge shows
Tx Rate 1500kbps Rx Rate 12Mbps
Tx Packet Rate 103000 Rx Packet Rate 112000
but in interface list interface to wireless bridge
Tx Rate 1500kbps Rx Rate 12Mbps
Tx Packet Rate 15000 Rx Packet Rate 17000

i think the problem with the speed is in the packet amount -is to much for the wireles bridge, any ideas?

is this packets per seconds? looks too much isnt it?