For my 2 I bed heaviest in the NE corner of each stall - where they always stand to pee. When I am using 100% pellets, this is where the bulk of them go.
If I'm using a mix, most of the pellets in this corner, shavings to the center.
My theory is that the favored spot was chosen because they can then look out the open Dutch door at the back to make sure nothing can sneak up on them whilst they are "occupied".
This is my second set of geldings who use the stalls the same way.
Second heaviest spot for either pellets or shavings is in the center - because they will walk out the stuff from that spot anyhow.
And I sweep the area in front of the stall doors - front & back - as well as beneath the water bucket & feed tub.