If I`m not mistaken, you mean the space for the Datanodes, in this case, in the datanodes configuration, the Supervision category and the datanode status monitoring thresholds, change to 70% or 80%. You have two types, warnings and critics.
Right, it seems not adjustable in percentage value (my cloudera MANAGER version is 5.14, it would be the same in 5.13 I remember).
As you know, monitoring thresholds colud be adjusted in absolute value at [Home > Configuration > Disk Space Thresholds].
I think it's sensible to specify them in absolute value because, usually the scaling factor of disk volume and those monitoring values does not match.
I noticed that from monitoring alert list, I can set Free Space Monitoring Percentage Thresholds.
I couldn't find other path to these setting though.
It may help if made clear where those adjustables are exposed I think.