Further to this:
TimF wrote up some additional testing:
Most interesting point:
The most interesting result is that in Test 3, 50 views were created which increased the ess00001.dat file to 411,041,792 bytes in Scenario 1 but in Scenario 2 the ess00001.dat file does not increase past 847,249,408 bytes. It seems to be using the empty space in the file to store the aggregate views.
that's exactly what I was seeing. Very strange how it's working.