We don't yet have any price indication for that new (rather ugly

IMHO) Clio.
Since the current Clio Hybrid's WLTP fuel consumption (4.3 l/100km) is nowhere near being achieved in practice (according to Spritmonitor, it's approximately 5.1 l/100km), that 3.9 l/100 km figure for the new one might also be a bit (too) optimistic.
The maximum boot space of the new Clio, at 391 liters, is identical to that of the outgoing Clio. So, like the current Clio, the hybrid has a boot capacity of (only) 254 liters. That's considerably smaller than the Jazz (304 liters) and the MG3 Hybrid (293 liters).
So...

your initial assumption seems a bit premature.