Pivot table problem

[jaya]

Hi,

I have a pivot table and pivot fields. I can select
different values from the pivot field dropdown and the
pivot table row values will change according to that.I
have five rows and they are all calculated members.
When i change the values/filter in the pivot fields,
i noticed that one more excel session is created. This
happens only when i have the calculated members as rows
which has the following calculation in the cube. I have 3
calculated members which have the following function in
the cube.
Iif([Measures].[Count]>0,
Percentile(SetToArray(Crossjoin(
FILTER(
DESCENDANTS([ClientHidden].currentmember,[ClientHidden].
[Analysis Name]),[Measures].[Count]<>0),
{[Measures].[Average]})),.9),
NULL)

The other 2 members have functions:
Median(Filter(
Descendants([ClientHidden].currentmember,[ClientHidden].
[Analysis Name]),
[Measures].[Count]<>0),[Measures].[Average])

When i have only these two members as rows the session is
not created..
What is the reason for this and how do i avoid creating
sessions?

-Jaya