Is there a trick for dimensioning in a 3D sketch? I finally had to create an "offset/through point" plane to dimension the true distance in X. It kept wanting to grab a vertex, edge, or face, and create a kittywompus dimension!
None-the-less its still very hard to get the exact location of your Dimension in 3D sketch. Try using Construction Geometry to not only control the sketch, but to help with your dimensions.