OP, if this is of any help I have the Rosa in medium (size 8 boot, 32 Lashed) and took some measurements for you.
These are all inside measurements of course. If the conversion from inches to cm is wrong, that's on Google, not me.
-From the inserts of toe strap: 4 1/2 inches (11.43 cm)
-Most narrow part: 4 1/8 inches (10.48 cm)
-Heel inside highback: 3 7/8 inches (9.84 cm)
Heel loop and gas pedal are adjustable. Three settings of 5/16 inches (.79 cm) and three screw holes respectively. I'll give you what are set on mine (size 8 boot remember) so you have an idea; I've the heel loop at the center setting ("1") and the gas pedal at the center setting.
-From lowest part of highback padding to edge of gas pedal: 10 3/16 inches (25.88 cm)