Rule to drop Bad Signal Strength in Mikrotik Access List

Hi .. I need to make a rule to drop my clients with bad signal strenght. I read that it is possible making a rule in access list. But im having a problem with this rule.

look the rule : MAC Address=null Interface=all Signal Strenght Range=-70..70 Authentication=no Forwarding=no

Look the problem :
The range i can put in access list is something like -70..70 or -80..80 . It doesnt work to me cause i want to drop clients with signal strength more then -80 for example , and when i put this range like -70..70 the client that have -80 are included in this range. I need something like this:
Drop range -30..-80 .. With this rule , only clientes with signal -30 to -80 can conect, but the range doesnt accept a negative value in second caracter -80.
Somebody help ..
Thanks.

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it works fine for me. ie. add one rule that allows good signal range, and then add second rule that DENIES EVERYTHING ELSE. just like firewall

It works for me ..Thank you very much bro .. I put range -120..-75 and its fine .. Thank you

hi
i am new in mikrotik. how can i create AP rule to denied everything ?