Yes, in most cases you should turn the height audio level up. I have mine set to +6. Usually, the higher your ceilings are, the higher the level should be increased.

Is it just trial and error or does the measurements determine how high u need to set it?

You need to find a Dolby Atmos source with distinct height channel audio playing and adjust the height audio level slider until it sounds good to your ears.

Ok nice one

Can’t say I’ve noticed any difference with the height audio 

How high are your ceilings? Are your ceilings flat with no obstruction?How far is the Arc from your ceiling? How far are you seated from the Arc?

I’m in a standard new build house with flat ceilings 

the arc just sits on a tv stand 

You need to sit fairly close to the Arc to hear the height channel speakers. I have flat 8 ft ceilings and my Arc is 6 ft from the ceiling. I need to sit from 5-8 ft from the Arc to hear the height channels well.

Does anyone know if Sonos is planning to release a new version of the Sonos Beam with Dolby Atmos support?

It’s probably unlikely since the current Beam is still extremely popular and they already offer a Dolby Atmos soundbar with the Sonos Arc.