Background eraser won't erase everything within brush circle even though settings maxed out.

I think there may be some confusion on how the Background eraser works—unlike the Eraser tool, which erases everything underneath the cursor—the Background Eraser is a color eraser tool.

The background eraser samples the color in the center of the brush, also called the hotspot, and deletes that color wherever it appears inside the brush. It also performs color extraction at the edges of any foreground objects, so that color halos are not visible if the foreground object is later pasted into another image.

—Erase parts of an image in Adobe Photoshop

~Barb

Michael-

It might be helpful if you could post a screen capture of what is happening.

Also, what is the Hardness setting of your Brush?