I hear a pretty dramatic difference. I have the height audio level set to +6. 

How tall are your ceilings? How far is the Arc from the ceiling? How far are you sitting from the Arc? What specific Dolby Atmos content are you testing?

In used load of atmos content on netflix

Arc is 170 cm from the ceiling and i am sitting 200 cm from the arc. 
 

Is your ceiling flat and without any obstruction like a ceiling fan?

You need to find Dolby Atmos content that has a specific scene with clearly defined height effects. Once you find it, test that scene while adjusting the height audio level. You should be able to hear a difference between the level being at 0 compared to +10. But +10 would probably be overkill.

FYI... just because content is in Dolby Atmos doesn’t mean the height channels are active all of the time.

You could also download this Dolby Atmos 5.1.2 test tones file and put it on a USB flash drive and plug it into your TV. Listen to the test tone from each channel and adjust the two height channels levels where they are at a similar volume as the other channels.
https://www.reddit.com/r/sonos/comments/hc21uu/dolby_atmos_512_test_video_file_download_link/

Sealing is flat square no obstacles 

will Test some more. Thanks