MDX -- Detect if ALL is selected in a dimension and adapt measure calculations based on this

Dear all,

I have the mdx below.

What I am trying to achieve is the following:

I have two filters : POS and Centre the constraint is that:

A) If the user selects a POS and then selects a Centre (it's always a single selection) then I calculate an average of an existing measure based on ALL the centers in that POS.

B) If the user selects ALL in the Centers filter then I shall calculate the average of the latter measure but this time for ALL the POS

I wrote the MDX below but I cannot get it to work. I think I am missing something regarding how the "ALL" attribute works.

 If I run the code with the filter: 

[TD_Centre].[Centre].AllMembers 

I seem to get condition B. But if I run with:

[TD_Centre].[Centre].&[All]

I get zeroes for KPIValue, KPINorm (ALLFED and ALLCENTRE are for testing purposes, I use it to see what KPINorm takes as value)

Then one more case, if I choose one center (which should indeed be condition A) by using:

[TD_Centre].[Centre].&[Some Center]

It still goes into condition B.

 WITH 
   MEMBER [Measures].[KPIValue] AS
		 		[Measures].[C12 Number Rate]
   MEMBER [Measures].[KPINorm] AS
			IIF([TD_Centre].[Service Centre].CurrentMember.Parent is null,
				FORMAT (
					AVG ([TD_Centre].[POS].Members,
							 [Measures].[KPIValue])
				, "Percent")
			,
				FORMAT (
				AVG ([TD_Centre].[Centre].Members, 
						[Measures].[KPIValue])
				, "Percent")
			)
   MEMBER [Measures].[ALLFED] AS
				FORMAT (
					AVG ([TD_entre].[POS].Members,
							 [Measures].[KPIValue])
				, "Percent")
   MEMBER [Measures].[ALLCENTRE] AS
				FORMAT (
				AVG ([TD_Centre].[Centre].Members, 
						[Measures].[KPIValue])
				, "Percent")
 SELECT 
	NON EMPTY { [Measures].[KPIValue], [Measures].[KPINorm],[Measures].[ALLFED],[Measures].[ALLCENTRE] } ON COLUMNS, 
	NON EMPTY { 
		(
			[TD_UneType].[UneType].[UneType].ALLMEMBERS * 
			[TD_C10Month].[C10Month].[C10 Month].ALLMEMBERS ) 
		 } DIMENSION PROPERTIES MEMBER_CAPTION, MEMBER_UNIQUE_NAME ON ROWS 
FROM ( 
	SELECT 
		( 
			{ 
				[TD_UneType].[Une Type].&[01], 
				[TD_UneType].[Une Type].&[02] 
			} 
		) ON COLUMNS 
	FROM 
		(
			SELECT (
					 { 
							[TD_Centre].[Centre].AllMembers 
					 } 
				   ) ON COLUMNS 
			FROM (
				 SELECT (
					 { 
						[TD_Centre].[POS].&[2210] 
					 } 
						) ON COLUMNS 
				 FROM (
						 SELECT (
									 { 
										[TD_C10Month].[C10Month].[C10 Month].&[385],
										[TD_C10Month].[C10Month].[C10 Month].&[386],
										[TD_C10Month].[C10Month].[C10 Month].&[387]
									 } 
								 ) ON COLUMNS 
						 FROM [MyCUBE]
				)
			)
		)
	) CELL PROPERTIES VALUE, BACK_COLOR, FORE_COLOR, 
	FORMATTED_VALUE, FORMAT_STRING, FONT_NAME, FONT_SIZE, FONT_FLAGS

If I am doing this wrong could somebody show me the right direction?

Thank you so much for your time

Miloud B.

Miloud Bel.