Look at the expressions in the Enable Conditional text boxes for the dimensions in the table.
For example =SubStringCount(Concat(_dimension, '|'), 'Region')
What happens is that there's a table with the dimension fields you can select in. The concat function creates a string that contains all the selected fields. Substringcount then checks if 'Region' is in that string. If it is then the complete expression returns 1 (=True, so show), otherwise 0 (=False, so hide). Does that help?
I used this expression for some of the fields in a straight table which are to be appeared in "Additional Fields" List Box & rest which should appear by default, for that I checked on "Always" appear option.
Also, I put the expression on straight table Properties --> general tab
Conditional ---> "=GetSelectedCount(_Dimension) >:0"
but it doesn't help.