I heard if to set fixed ACK timeout and fixed rate, delays on big load of channel will not grows.
I have link on 25 km with SR5 cards on both ends and i tried to test this
but it seems doesnt working.
According to manual i configured ACK to 203(5GHz link) and rate to 18Mbit
But i noticed if i set ACK to 100 or even 10 
my link still working like before.
Can anyone suggest something?
is nstreme enabled?
Yes, nstream and polling enabled.
then that would be the reason setting different ack values has no effect.