Matrix using left outer join to display all data from one table and linked data from another.

Hello, new boy here.

I hope this makes sense:

I`m trying to create a matrix in my report which shows all item product groups down the side and all salesmen across the top (I`ve done this). I want the values to be taken from a sales table using a date range from a slicer but when I bring the values in to the matrix the rows and columns shrink so that only the salesmen and product groups are shown where there is a sales value but I want all groups and salemen to be shown whether there is sales data or not.

The two tables are linked by a product group/salemen field I`ve created in both tables, I`ve tried to create the relationship to be the group/salesmen table at the top and the sales table at the bottom but when I save this as a one to many cardinality it flips around to be a many to one which I`m assuming is the issue. As I understand it by default the relationship is a left outer join with the top table being the left.