Here’s a solution to my original problem, and some documentation for the “Text” parameters in Schematic Setup > Formatting.
In the “Text” area:
Default text size:
This provides a starting text height for:
The Text Height property of text corresponds to the height of a capital letter, not counting the thickness of the lines used to draw the letter. Actual text will occupy more vertical height due to the thickness of the lines, and due to descenders on lower case letters, and overbars on negated signals.
Text offset ratio:
Pertains to local labels. This specifies the distance of the label from the wire according to the following formula.
Actual distance of wire to label = TextHeight * (TextOffsetRatioPct +16.7)/100
… again, ignoring thickness of the lines of the letters and the wire and also ignoring descenders.
Global Label Size:
This defines the size of the box shape around a global label.
GlobalLabelBoxHeight = TextHeightmm * (GlobalLabelSizePct * 2 + 125) / 100
We typically want global labels to be able to fit adjacent to each other when attached to a component that may have leads spaced (on the schematic) at 100 mil (2.54 mm) pitch. Consequently, the height of global labels should not exceed a maximum height of 2.54 mm.
We also want sufficient space around the text so that overbars do not overlap the box, as that makes them difficult to see. For example, a Global Label Size = 25% results in overlap of the overbar with the box, so is hard to read.
Instead, the default GlobalLabelSizePct is 37.5%. With the standard default height set for text at 1.27 mm, the Global label box height is exactly 2.54 mm, so that the top and bottom lines of the boxes of adjacent global labels overlap exactly and don’t double up visually. This reduces visual conflict with the overbars, and gives those overbars maximum space, given the height constraint.