Ancestry Grouping Crisis?!!

[Merry]

So, I've created a few groups (4) and now I've got despondent/confused.

My 4th group has 11 people in it. Most of these individuals either have no tree or a tree of Americans who I don't recognise. However, two people in the group have a Common Ancestor leaf thing. I clicked one of these and then realised the owner is someone I used to email about FH about ten years ago so I know who he is related to (he is on my tree!) and his tree on Ancestry reflects this. Our common ancestors are my FMM's parents. He is my 3rd cousin once removed.

As I looked at this one first, I named the group after this branch of my tree.

I then looked at the tree of the other Common Ancestor match, only to find our common ancestor is in a completely different part of my tree, so I'm confused. Instead of being connected via my FM line, they are connected via my FF line in a different part of the country. This person is my 5th cousin once removed.

They both show up as potentially being 4th-6th cousins, so that part seams reasonable.

So, how is this DNA shared when one person is connected through my FM and the other through my FF? I feel like I now have no idea about the other people in the group and I the name of the group is now misleading.

Advice please