I have only cooked on a UDS once so far, so your getting those drippings mixed in as well.
But yes, since lump is wood, I use less wood chunks in my WSM when using mostly lump.
I usually do a 50/50 mix of briquettes and lump plus 3 fist size chunks. I put the lump on the bottom, so when the chunks are gone, I still have a little smoke from the lump.
My .02