Craig,
You may try tweeking the diameter of the dovetail tool a little. In the tool manager, If you make the tool diameter larger, the tool will want to comp out, thus making the part bigger, and making the joint tighter.
Note: Although you are making the tool diameter larger in the tool manager, the tool is staying the same size
we use 1/2" Baltic Birch and I have set up the dovetail bit as 0.395" diameter. Seems to be working good. I tried to crank it up to 0.400" but hen they turn a bit tight. Personally I would rather get them tight but for large production and different ppl putting them together it's better to use the first diameter.
Also if that's the first time you are cutting them make sure the dovetail goes a hair deeper in the material. It'll eliminate a gap that appears on the inside when you try to assemble it.