When a custom metrics targets specific databases then only those database should be listed on the Analysis tab
Currently a custom metric is listed in the left most list box and the databases are in the right most. Some custom metrics are specific to a single database or a specific group of databases.
In either of these cases the database list in the last list box could be filtered to be only the databases that the metric relates to. This would save clicks and shorten the time taken to get to view the analysis trace.
Related to this, even if a custom metric is specific to a database or list of databases, please default the selected database to (All).
I have a custom metric that is measuring a large and fast growing table in one particular database - having the Analysis page default to 'master' means more clicks.