@ivmikh - Discussion related to this topic, and other helpful context can be found in this forum post. I am not completely sure as to exactly why the reported volume for a rounded base segment is being underestimated by the labware editor application (compared to the theoretical volume based on face-value geometry), but this volume calculation (from labware editor) is not what VENUS uses at runtime to calculate liquid following, when that is toggled on.
Rather, VENUS does a separate calculation for liquid following distance based off of the starting height of the aspiration and the mixture of container segment geometries the requested volume.
More accurate techniques for using channels to measure and estimate remaining volumes in containers is discussed in the linked thread.
-Nick