I have setup mangle rules for download and upload and Queue tree for my network. Qos is not working correctly in my case. Well problem is that I have no stable internet speed, sometimes is 35Mb and sometimes is 25Mb and sometimes is somewhere in the middle. So I cant set correct max-limit value in Queue tree for download. If I set download max-limit value to 25Mb and I currently could reach 35Mb everything works OK, I have NO problem at all, I can see that router queued packets in WinBox. When I set download max-limit value to 35Mb and Internet speed goes slow to lower value, maybe to 25Mb than nothing works correctly anymore, there are no queued packets in WinBox.

Value limit-at do not have any influence at all.
If I set limit-at to 10M and max-limit to 35Mb and internet speed is 25Mb nothing is working correctly there are no queued packets.
If I set limit-at to 10M and max-limit to 25Mb and internet speed is 35Mb everything works ok, router is queued packets.

Please, is there a way to make router to queued packets on limit-at instead of only on max-limit value?
Thanks for help.