Adaptive threshold metrics setting

Hi,

I have been trying to set the adaptive metrics in EM12c, but not quite sure if I am doing it right.  Warning and critical thresholds were not set during initial set up of adaptive metrics.  Over time I get alerts on metrics which have reached the default significance level and noticed that readonly values are now set.  As far as alerting is concerned, this is good as this was my expectation of the adaptive behavior.  But regarding the threshold values, can someone explain when and how these are set?  Do these values change depending on the load in the database?