Excuse me for answering in English as my French spelling is not good.
You ask if it's true that quad boards (and other multifin boards) can be used with bigger volumes than their single fin equivalents.
The answer is yes.
This is because the single fin board can over-power by virtue of its volume and because of its fin 'lift'.
Part of fin lift is the leverage of the fin on the hull under typical sideways load – and the longer the fin, the sooner you become over-powered in windy weather.
With a pair or 'cluster' of fins – as in the twin fin or quad fin set up – you have plenty of fin area to get you upwind and to secure the back foot against the sideways loads of the rig, but there is less leverage, as each fin is so short.
So you can stay on a bigger (more voluminous) board for longer as the wind increases.
A wide or wide-tailed board will still start to bounce in truly windy weather, but the quad fin board will stay controllable for longer.
What this means in practical terms is you now need fewer boards in your typical board quiver. And your smallest board, can now be bigger than it traditionally was with a single fin. Adding four fins to a board has increased its useful sail carrying range.