Setting visibility of fields for context sensitive DFF segment?

Summary:

We have a requirement to control the display of context-sensitive segments within the HRT_PROFILE_ITEMS DFF.

At present, the context is the Profile Type - this determines which fields are displayed.

However, we want to further control display of the segments based on preceding segments, essentially another level of context sensitivity within an already context-sensitive segment.

We suspect this can only be achieved by EL but have so far been unable to achieve the required outcome.

Content (required):

HRT_PROFILE_ITEMS has been configured with a context-sensitive segment of PERSON_PROFESSION

Segment20: Always (uses Yes / No value set)