Reply to "flat brisket with a lot of fat"

Just put your probe in the thick part of the flat.

That is your temp concern.

You can carve out some of the fat wedge between point and flat and cook them together.

Here is a good pictorial from the Cookshack open forum.
Brisket Trimming

You can't overcook the point.

When the flat is done,you can always toss the point back in the cooker,until it suits you.