MDX - Use Aggregate on a CROSSJOINed multi-dimensional set to return a grand total row - mdx

Question

I raised a ticket on grand totals when filtering ages ago and I used the proposed solution yesterday to get one dimension working:
WITH
SET [FilteredSet] AS
{
FILTER([CDR].[CDR].Members,([CDR].[CDR].CURRENTMEMBER.MEMBERVALUE="70648") OR ([CDR].[CDR].CURRENTMEMBER.MEMBERVALUE="70646"))
}
MEMBER [CDR].[CDR].[Test] AS Aggregate([FilteredSet])
SELECT NON EMPTY {[Measures].[CS01.TenorTotal] } ON COLUMNS, NON EMPTY {[FilteredSet], [CDR].[CDR].[Test]} ON ROWS FROM [TraderCube] WHERE ([Date].[Date].[2022-04-01],[Epoch].[Epoch].[Branch].[master].[17])
(Other ticket with useful info)
MDX - Grand total missing when filtering
And as I expand the test query (to get it all working and I then expand the C# code to add it) I note that this works:
WITH
SET [FilteredSet] AS
{
FILTER(CROSSJOIN(HIERARCHIZE(DRILLDOWNLEVEL([CDR].[CDR].[ALL].[AllMember]),POST),HIERARCHIZE(DRILLDOWNLEVEL([Book].[Book].[ALL].[AllMember]),POST)),(LEFT([CDR].[CDR].CURRENTMEMBER.MEMBERVALUE,2)="66") )
}
SELECT NON EMPTY {[Measures].[CS01.TenorTotal] } ON COLUMNS, NON EMPTY {[FilteredSet]} ON ROWS FROM [TraderCube] WHERE ([Date].[Date].[2022-04-01],[Epoch].[Epoch].[Branch].[master].[17])
But we will often filter on the 2nd (or 3rd, 4th etc) dimension, like so and the total (AllMember) is filtered out from Book as it does match the INSTR comparisons.
How do I get my Aggregate MEMBER to work properly here? I've placed [?] in position as I can get this sort of setup to work on one dimension (E.g. [CDR] as shown in first code block) but here the query returns [CDR] and then the [Book] members that match and I want to 'glue' my Agregate MEMBER [?] of the measure as a grand total.
WITH
SET [FilteredSet] AS
{
FILTER(CROSSJOIN(HIERARCHIZE(DRILLDOWNLEVEL([CDR].[CDR].[ALL].[AllMember]),POST),HIERARCHIZE(DRILLDOWNLEVEL([Book].[Book].[ALL].[AllMember]),POST)),(LEFT([CDR].[CDR].CURRENTMEMBER.MEMBERVALUE,2)="66")
AND (INSTR([Book].[Book].CURRENTMEMBER.MEMBERVALUE,"72")>0 OR INSTR([Book].[Book].CURRENTMEMBER.MEMBERVALUE,"73")>0))
}
MEMBER [?] AS Aggregate([FilteredSet])
SELECT NON EMPTY {[Measures].[CS01.TenorTotal] } ON COLUMNS, NON EMPTY {[FilteredSet], [?]} ON ROWS FROM [TraderCube] WHERE ([Date].[Date].[2022-04-01],[Epoch].[Epoch].[Branch].[master].[17])
Current MDX error back is:
'The 2 objects do not have the same dimensionality: [[CDR], [Book]] and [[Measures]]'
Thanks to more advanced MDX-ers out there! :)
Leigh Tilley
TilleyTech Ltd
P.S. Sorry no screenshots...client browser trackers would detect it and I'd get in trouble!