Value "Noise Floor Threshold" don't work

Hello to all forum,
I have 3 years as a WISP with a network of 500 clients and I would like to prevent unauthorized people from connecting to the network and make my “ack timeout” up to 408 and CCQ down a lot.
I tried to implement the value -80 “noise floor trheshold” but it does not work! this setup no work in versions 3.27 ,3.13,3.24,etc.. Why not?
I not want implement access list because take me a long time to configure all AP’s!
There is another way to prevent that users with values of very bad signal and noise can not connect?

Thanks in advance,

That: http://forum.mikrotik.com/t/rule-to-drop-bad-signal-strength-in-mikrotik-access-list/30156/1 response to my question!!!
This is a solution very good for me.