combining reports with different driving objects (reporting)

I have a simple report for users of activities, which I have made using subject area Activity history (Analytics). It has the following standard columns: Calendar Year, Calendar Month, Calendar Week, Subject, Owner, Account, Contact, Start time, End time, Address, City

As historical report does not show data entered during the past 24 hours or so, the users want another report that retrieves the information real-time. So I am trying to create the same report using Activity subject area (Reporting).

Apparently these two act a bit differently, in the real-time report the Account and contact fields act as a filters, so if I choose Account name in the report, there are less results than without it. If I further choose Contact, the results are even less than that.