A two point calibration will scale your distances unless something has changed in the software. They don't clearly state?ÿwhat happens with 1, 2, 3, and 4+ point calibrations ?ÿin the Access documentation but at one point they do say that any horizontal transformation using two or more points will have a simple 4 - parameter Helmert performed consisting of two translations, a rotation, and a scale.
They also state in two different areas that Trimble recommends using four or more calibration points that are evenly distributed and are outside the area to be surveyed, as you would with GCP for aerials (same principals apply).
I should add that there are settings in the Survey Style that will affect the behavior of the software, as will whether a projection and / or datum is assigned to the project. My comments on this subject apply to the way I work and the parameters that I use.