So I just happened to be browsing the Trek Hybrid FX geo chart (see below) and it has the same whacky situation.
ST difference from S to XL is 19cm
ETT difference from S to XL is 4.5cm?
So with these whacky geometries what happens with the bigger sizes to accomodate the minimal increase in ETT length? Taller people naturally have longer arms and torsos. So do they make you more hunched over to negate the minimal increase in ETT?