When you add subgrids to a contact or account (e.g. opportunities, activities, cases, etc.), it only gives you the ability to show records that are directly related to the parent. It would be great if this mirrored the functionalty in the normal opportunities grid (left nav) where it shows records that are owned by the current record, and records related to any child records.
Thank you for your suggestion. We will consider taking this up in a future release.
Additionally you can implement it as Advanced Find based System Views, this will allow to have Views that span multiple not directly related entities based on a custom query AND ability to place them on forms as Sub Grids. I have similar request : https://ideas.dynamics.com/ideas/dynamics-crm/ID0004213