Hi, I never got a reply from Focal.
I read loads of posts about Atmos Upfiring Speaker positioning and there was no right answer on calculating what's best. Understandably it seems that people position their Atmos upfiring speakers at angles at which they think sounds best for them.
It's good that the Focal Sib Evo actually allow 10 degrees of tilt as many people seem to have to wedge their speakers.
I even went as far as drawing out the measurements of my room and using a protractor worked out that sitting approximately 255cm away from the speakers at an ear height of 95cm with a ceiling height of 240cm the speakers would have to be tilted further forward than the stand allows (I think max is 60 degrees) to get a direct bounce. I'm sure though at this angle it would make the sound too directional?
To be honest I couldn't really hear a noticeable difference when tilting the speakers and in the end I decided after watching this
video (see 2:53) that if Dolby had recommended an angle of 70 degrees they must have done this for a reason. The diagram in this video shows the sound dispersing/reflecting at a large enough angle to cover my own seating position.
I'm sure Dolby must have a good idea of how tall the average ceiling is and that the 70 degree angle would cover the majority of people's home environments. So I have tilted my Focal's back to the recommended position (70 degrees) as per the Hip Evo Stand manual.
I also put the distance from the top of the Atmos speakers to the ceiling into my Denon (136cm) and increased the distance from the Atmos speakers to the seated position to take into account the travel to the ceiling and bounce back down (385cm). I've also raised the Atmos Speakers by 2 dB.
I need to get round to watching some decent Atmos soundtrack films and have picked up John Wick, Mad Max and Unbroken which are all meant to be really good.
Let us know if you learn anything more.