The documentation for this portlet http://www.atlassian.com/software/jira/docs/v3.12.3/twodimfilterstats_portlet.html does not specify the custom fields that are supported.

A customer has changed their workflow to use this portlet with a numerical custom field. There is no documentation that this portlet does not support numerical fields, only these custom field types: 'Group picker', 'Multi select', 'User picker', 'Select list' and 'Version picker' custom field type.

The customer is midway into a project assuming numeric custom fields could be used.