Trouble associating 2 RB600 and XR5 cards 20 mile hop

I have (2) RB600 with (1) XR5 radio in each. I am trying to get them associated and at times I can. I want to set the ack-timeout but when I do I do not see the change when I do a /interface wireless print. How do I get the value for ack-timeout on a RB600? Any other ideas out there for a 20 mile hop?

Can you say more about your configuration?

Is the link line of sight? What kind of dish? What hight are the antennas?