Is there a setting that will tell notes to be added to a container in a grid instead of straight line?
I don’t believe so. $CleanupAction only applies to agents/smart adornments, and the View → Arrange → Cleanup function is only applied directly (‘live’) via the UI.
Begs the question how the software understands the users intent which is likely a variation “fitting on screen better” though the number of items (closeness of packing?) and size of screen vary. I note this only as I was thinking on the practicality of doing this as a container attribute (doc setting?).
You could set $Xpos and $Ypos in the container’s OnAdd action. For example:
$MyCol=$SiblingOrder%5; $Xpos=5* $MyCol; $Ypos=3*(floor($SiblingOrder/5))
The % operator is modulo or remainder: If $SiblingOrder is 23, $SiblingOrder%5 is 3.