What equipment are you using ?
Unless you dont have congestion, i would recommand to use AMR_FR and not AMR_HR.
You can trigger AMR_HR @Busy Hour to gain capacity through your network.
Normally, each vendor have an algorithm that will switch to HR in case there is Load (for instance at 70% ) in the cell.Ones the cell is not loaded over this , it will use AMR_FR. This is an usefull features but be carefull to the dynamic of the algorithm, again it all depends on the vendor.
You might have to set up as well the levels for switching from HR to FR and FR to HR (like A_QUAL_CA_FR_HR and A_QUAL_CA_HR_FR)
Hope that help