Ah! You are using the Reports module (generates emails and HTML), not the Excel Reports (generates Microsoft Excel documents). The data for those Reports is stored in three database tables,
ReportInstanes - Each run report will correspond to a row here.
ReportInstancePoints - Each run report will insert rows for all the points in its context.
ReportInstancePointData - Each point in a run report will store its data for that report here.
So the finished product isn't stored as a composed item unless you email it.
One thing the Reports module enables that is cool is copying & customizing the reportChart.ftl file to something simpler, then you can get data formatted however you like over HTTP from a URL endpoint for each finished report, such as mangoUrl/reportChart.shtm?instanceId=1
The modules' files should be in Mango/web/modules/reports