Think of the base surface and the text being made of stretchy or compressible rubber. Consider the text as lying down on the rubber sheet. The Flow command does some math, translations, scaling, rotation, alignment...
The base surface is stretched and curved to match a section of the torus, and the text stretches to match.

- Brian

The user may want to cut out a section of the torus where the letters are to be located, and unfold the dimensions, (like unwrapping), to make the base suface, with a copy to be placed below the text. The target of the flow is the unwrapped section of torus. This would preserve some of the spacings.

The torus section could be a section of its outer semi-circular surface...