If you are adding metrics to a Project Office site that calculate their value using a Project Summary report, you should ensure that Exclude from Reports stays selected in the hidden Project Statement in the Project Office. This is to ensure that there are no double counting of the Project Office.
You should also ensure that Include all sub-sites and Enable Site Filters are turned off in the Project Office Summary report and any other report that reports on metrics in the Project Office.
To understand the distinction here, examine the screenshot below. Both reports are generated using the Template Projects - Projects Summary report. The Project Summaries report on the bottom rolls up information from the sites beneath the Project Office. It does not report on the Project Office because the Project Statement has Exclude from Reports selected. This report feeds the Project Metrics list in the Project Office with some of its data.
The Project Office Summary report on the top reports on the Project Office, even though Exclude from Reports is selected in the Project Statement. This is because Enable Site Filters is turned off in the report. It only reports on the Project Office because Include all sub-sites is also turned off.