AS View Query

Hi,
I have a customer whose traffic flow comes almost exclusively from one address and runs for about 14 hours out of 24 - it's a backup process.
If i look at an hourly traffic report for the customer, the figure pretty much matches the last hour report for the AS where the traffic is sourced from just as expected - averages out at 8 meg or more.
If i look at the 24 hour traffic report for the customer, it shows an average of 5.5meg which is correct.
However, the last day report for the AS seems to drop right down to under 2meg.

Is the AS view traffic statistics averaged out in a different way to the ip group traffic statistics? Can you explain why we see the difference on the 24 hour report?

Thanks for your help.
Richard