I looked at the video you provided, and the average x/y jitter in the video appears to be on the level of a few centimeters. This is about as good as the current demo system can get, but please remember, that this is primarily a demo system. If you need more precision than that, it may be worthwhile to have a more thorough discussion about implementing a custom solution to fit your specific needs. For a more detailed explanation of expected system accuracy, please refer to the following post: What accuracy can be achieved?.
As for the static height that you mentioned, that is a symptom of your configuration. Because of the way the current location algorithm works, a tag that manages to get on a plane that intersects all of the anchors will never be able to leave that plane. As all of your anchors are at the same height, this means that any tag that reaches that height will be locked into that height. There are a couple ways to prevent this issue from occurring:
You can make sure that all your anchors do not lie on the same plane. In your scenario, this means that you would need to put at least one anchor at a different height than the others. In general, you will want to increase the z-diversity in your anchors if you want to improve the preciseness of the tracking of the z-coordinate of a tag’s position, so a better solution would be to set up half of your anchors at one height and half at another height.
You can set up the bounding box for the tag locations such that the tag will never be able to reach the plane intersecting all of your anchors. In your situation, as all of your anchors are at a height of 2.683m, you will want to set your “z_max” value in your configuration file to something lower than that, such as 2.5m. By doing this, the tag will always be forced below the height of all of your anchors, so this little oddity in the location tracking algorithm will never be able to take effect.