The data in AirWave is stored in 5 min bucket intervals. When you see a graph for any time period, the X-axis is divided by 240 data points (AFAIK).
So, when you see a graph for a day (for example), there are 1440 buckets of data and 6 buckets are combined to get 240 data points. The Blue graph is average of the 6 buckets and the yellow is max in those 6 buckets.
Similarly, when you see a graph for week there are 7x1440 buckets of data and 42 buckets are combined for each data point to make it 240 data points on the graph. The Average and Max for each data point is based on the 42 buckets.
Thats the reason, for shorter periods of time, Ave and Max would be similar and the Average decreases, the longer the graph is taken.