Ok this could work but there is 1 more complication, there is a total for each row of the matrix so I would need a total for each member of the row group and then lookup up the correct total based on the row group member.
Revising what I put earlier, that alters to:
=Sum(current column group member and row group member)/Sum(all column group members for current row group member)*100
How could I achieve this?
Or am I missing the point? I am honestly so confused by this, Excel does it in 2 clicks and this seems so complicated.