I've read https://support.circleci.com/hc/en-us/articles/115014004948?input_string=coverage and other documentation you have for coverage reports and have implemented coverage to be stored as artifacts.
However I find this "artifact way" almost impossible to use, as there is no way to see the evolution of the metric over some time or at least between two jobs.
I would like to suggest to introduce a feature "custom metrics" which would allow a job to emit customer defined [numerical] metrics (so we can use it for more than just coverage) which would then will be presented in the job results and also in the project insights, so its evolution can be seen.
Or maybe have a page or a section in the job results page to compare the job metrics to another one, e.g. release/1.0.1 to release/1.0.0.