I usually bury now since I no longer have an offset. With the old offset, I'd go right on top. With the UDS though, I have hinged grates so in theory I could add wood right on top if I wanted to. Haven't tried it yet..
In the UDS I bury 4-5 fist sized pieces and drop on on top when the pork hits the pit.
If I'm cooking a brisket on the UDS I take a piece of Mesquite about 3" across and 8 " tall it goes into the middle standing on end and the lump gets packed around it. It gives me just the right amount of smoke over the whole cook.
Buried initially, toss upon the fire when needed to stoke more smoke. I also have been known to place a chunk or two in the chimney starter when building the initial fire. No rules, do whatever you want.
For my UDS, when I load up the basket, I'll end up using it for multiple different cooks without refreshing, so I try to make sure there is wood throughout, so each cook will get relatively even smoke.