I suspect that Datacad is using the individual font's definition of baseline x-height and caps height for bottom, center and top. Our drafting idea of text-height is typically the same as caps height, where computer font-sizes are typically descender-to-ascender height. One problem is often a font may actually output above or below any of these values -- complicated by the Operating System, the display drivers and the printer-drivers -- and some are actually defined exceeding the caps height of the ascender-descender height, particularly "Architect's lettering" fonts that are drawn on the bias and exaggerated. Some font are also designed with built-in "leading" above or below the ascender=descender to create more "white space" between the lines -- similar to Datacad line-factor.
I find that when looking at a new .ttf-font for use in construction drawings that I have to do a quick style-sheet to look at the actual aspect-factor and spacing-factor of the font as it plots out to compare text-heights versus font point-size or "text size". Typically the dimension-command will osnap to the baseline and cap-height to actually measure the output accurately for comparison. Point-size is roughly similar to the dimension at 1.0 factor and aspect from baseline-to-baseline.
Also the larger the desired text output, the tighter the aspect and spacing factor adjustment to look "correct". The particular font that is my office-standard-text for construction drawings is an architect's-style lettering that is modified to aspect 1.25 and factor 0.85 to look like manual lettering; typically in shift-lock CAPS. If I want "regular" mixed-caps (caps and lower-case), I have to increase the text-height to insure the lower-case remains legible. I don't use Datacad's "all-caps" since I prefer having more control over the text; like brand-names in mixed-caps when the body-text is all-caps, abbreviations or lower-case "x" in (2x4), etc...
I find that using "architect's-style" lettering, generous line-weight variations and overshoots enlivens CAD drawings for a hand-crafted architectural feel -- versus the rather sterile default Autocad-style -- especially for drawings used by clients and non-professionals. I also have SketchUp Layout set-up similarly for a hand-rendered b&w presentation.
I find that Datacad's "Datacad"-font, "Heavyhand" and "Graphite" fonts are very useful. For a contrast for specs or blocks of text the "Gentium", "Old-style" and "Goudy" font-familes have a comfortable serifed-look. "Apple Garamond Light" and "Franklin Gothic Light" have reputations for being very ink-jet ink efficient.
I also LOVE typewriter fonts for their old-fashioned appearance, "F25 Executive" being a personal favorite for correspondence and transmittals.