'It appears that your other boot environments are so small that the total used vs your current boot environment are almost the same'
English is my first language but I am struggling to parse this statement and observe the same flawed behaviour.
Here I have a single boot environment (11.2-U2) which consumes 3.9GB so the total used vs my current boot environment is, by definition, the same. As I only have a 8GB boot device, this might potentially be an issue.
Quite why it consumes 3.9GB instead of c. 800MB is not clear but I won't be logging a bug if that is their considered response.