This seems to be true, l changed my coolant yesterday and after removing the bottom radiator hose (removing the grille there's a small hose at the bottom left) and also the thermostat hose plus the bleed screw etc it only took 6.5 litres to refill it.
The coolant l drained looked OK (not discoloured and still tested good) so l suppose 3.25 litres of new antifreeze at 50% will keep it protected for a while.