Make Avg() on filtered data

[gbim]

Hi,

I need help in this problem.
For example I have the query below in Web Components
Calendar Price Avg
200505 50
200506 23
200507 45
200508 33
200509 23
200510 56
200511 32
200512 12 30,75 <<--- Calculated Member

Avg = (12 + 32 + 56 + 23) / 4 = 30,75

Calculated Member MDX
if([Calendar].CurrentMember.Level.Ordinal=0,null,Avg([Calendar].Lag(3):[Calendar], [Measures].[Price]))

Everything works fine, but when I filter some data in Web Componentes the calculation needs to be made in filtered data...

Calendar Price Avg
200505 50
200506 23
200507 45
200508 33
200512 12 30,75 <<--- Wrong value

The value 30,75 is wrong.
The correct value should be 28,25
Avg = (12 + 33 + 45 + 23) / 4 = 28,25

Anyone knows if it's possible to make the average with the filtered data ?

Thanks !