Coupon include products in sub categories?

[dsrpmedia]

I have a shop with master categories and subcategories

there are no products in the master categories, only the sub categories.

each master category has sever dozen sub categories

I am trying to make a coupon using the native coupon feature for a master category - but it is not including the children (sub categories)
Is there any way to have sub categories included when making a category specific coupon?

any help would be greatly appreciated