That's actually pretty good. Their data (https://youtu.be/AjYyjQKW-pU?t=198) is consistent with my experience: +/- 6 dB or more depending on who is holding the remote and how they hold it. Range checks are not very reproducible and if you start worrying about reproducibility your time is better spent setting up a basic outdoor 3m test if you don't have a chamber. Most of the "hold to your chin" effect is just "try holding it a different way".