The number of flights per hour is not the only reason to chose band-boxing/splitting sectors. ("group/de-group", AWCI)
The nature of flows is another one.
If the expected traffic is due to be made of vertical flows (departures from/arrivals to London, Brussels, Paris, ...) then the splitting scheme will not be the same as if the traffic is due to be leveled on a given sector (several flows to be crossed at the same level).
Depending on the hours of the day, a mix of configurations is used and can be changed up to several times per hour.
ATFM can be a factor too : if we need a protection (a SLAP, Slot Allocation Procedure, provided by CFMU) on a sector, then said sector must be split. Don't know wether this is a French or a European rule.
Many other reasons (CBs, turbulence, technical, military activity,...) must be taken into account.
We (the French) couldn't deal with more than 12.000 flights per day without a bit of flexibility...
I reckon France is neither more, nor less flexible than Spain, MUAC, or any other ANSP in Europe.