Assemblies - 2D details - hidden lines

Presently any Assembly of groups that we detail is showing hidden lines irrespective of detailstyle settings.

We are able to control the viewing of hidden lines in single parts and groups via the detailstyle settngs, but with Assemblies we are not able to turn off hidden lines although it is set to not show in the detailstyle.

Assemblies (a collection of groups) is new to us and the complexity of the Assembly means we must not show hidden lines, how is this possible?