It seems that the per model setting for infill is treated like it's own object and so it inherits the same
4 walls, 6 top layers and 4 bottom from the model, which means layer view shows 8 walls are created.
This increases time and material used. Besides adding the Infill setting for 20%, I need to add walls, top and
bottom layers and set them all to 0. If you had 4 walls set for infill, and the infill box is within the model, layer
view will show the model use 4 walls, and then you'll see the infill area with it's own 4 walls.