How to setup a Context Sensitive DFF to work based on GL Journal Category?

Summary:

How to setup a Context Sensitive DFF to work based on GL Journal Category?

Content (please ensure you mask any confidential information):

We have a requirement to configure a context sensitive DFF to appear based on specific GL Journal Category value. We have configured this to work on the journal line, but it is not working as expected.
The issue we have is that the user must populate the context value at the line level, which in turn would display all the DFF values that needs populating. Please see the uploaded screenshot.
But user can select the context value on the line for any Journal Category. It cannot be restricted to work on specific Journal Category value.