ΔE 11.2, fair: the same colour family, but not a straight swap. Transparent Sepia is more saturated, cooler than Soft Tone. They are different kinds of paint: Army Painter Soft Tone is a wash/shade and Green Stuff World Transparent Sepia is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Transparent Sepia is more saturated, cooler than Soft Tone. They are different kinds of paint.
The same difference applies the other way round: Soft Tone is more muted, warmer.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Soft Tone on the colour wheel See Transparent Sepia on the colour wheel
All matches: Soft Tone equivalents · Transparent Sepia equivalents