Logic Pro X: change grid value

Apologies is this has been covered before, but I couldn't find it. I have Time Signature/Division checked in the custom display menu. When I change the grid value in the display, it changes it in the Piano Roll but not in the main window above the Piano Roll window. This is so if I zoom out or in, doesn't make a difference. The main window always shows 4 divisions in each bar.

I'm sure I'm missing something here.