Quite often the smoke, which is heavy initially will peter out to near invisibility, depending upon lighting and wind. Sometimes placing a black object (painted cardboard) near the vent will allow you to see the finest of wisps. I cut my wood into 1, 2, and 3 ounce pieces. Yes, one large chunk will or should last longer than a couple of small pieces. But if your meat has reached an IT of 140 degrees, the exterior is sufficiently glazed overs that the cells can no longer absorb smoke. From that point on, the smoke particulates just sort of layer up on the surface and it does get somewhat bitter.
The result you are looking for is are you and your family happy with the final product. And if you want to extend the smoke you could try wrapping the wood in foil and poke a hole or two in the foil. Just remember some of this is trial and error.
Happy Independence day.