Thanks a lot @Alexandre That is the answer I was afraid about ;-) So E4 commercial presentation is a bit misleading when they announce 1200Mbps throughput. They should explicitly mention you need to...

Hi team, E4 presentation annouces 1200 Mbps on Wifi while the E4 device cannot be fed with more than 100Mbps through its Internet port... The consequence is that I get a maximum of 88Mbps on the E4...