As stated in GHS-7652, in our company Epics stand for big features. So for now we use an Epic for each sub-feature and using labels for associating it to a main feature.
Sometimes - working on main releases and branches - it occurs that a Story affects more than one sub-feature. But for now it is not possible to actually associate that Story to more than one Epics (via Epic Link).
(It was possible doing that with the "old" Epic/Theme labels though.)