I use subreports, but if I understood you correctly you might be able to to accomplish the same thing with 2 groups. Here is my thought
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Group 1 Header Fibre
Group 2 Header Id
Details
Group 2 Footer - suppress or not as needed
Group 1 Footer - suppress or not as needed
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I find that adding subreports can have an impact on performance as wl as introduce other complications so if I can design the layout without them I do.
Regards,
John W.