Sonos ARC: I don't hear the surround effect behind or overhead ...

FYI… to hear the height channel effects the best from Dolby Atmos content, ideally you want to be in a room with 8-9 foot flat ceilings and sit about 5-7 feet away from the Arc. Also be sure to adjust the Height Audio level higher under the Surround Audio settings in the Sonos app. I have mine set to +6.

Have a nice Sunday! Thanks for everything!
I'll try later (a friend finally comes home, so I do this via iOS and let you know and update you).
A curiosity please: since you have set everything well (I imagine even after having studied everything well, given your great preparation ...), what can I expect as surround effects, even though I am aware that we always talk about "virtual audio" why don't i have physical speakers? Can I expect top-down audio, side-to-ear audio? For audio from behind your head, I guess I need the physical speakers placed behind it ... Although the demo from the SONOS website demonstrates the ability to wrap 360 ° audio with the soundbar alone … 

Much of the experience is under the control of the video’s director and the expectations of the viewer. New surround users expect to be smacked in the back of the head by the surround and will be disappointed if the first film they play is providing only subtle ambient sounds, not BAM, BOOM, CRASH. Older films, created before Atmos existed, will not provide much of a 3D effect.

If the listener is well placed with respect to the bar and the room is not mucking with things too much -- and the source material is cooperating -- the rear speakers are optional. In typical living spaces, with typical source material and playback equipment, rear speakers are a big plus.

In controlled situations interesting things can happen. I was at trade show and a representative approached me from the rear and introduced himself. I turned to face him and there was no one there.