@tymonx-
Thanks again for the responses, I didn't get a notification about them, otherwise I would have responded a bit faster 🙂
The UVM Packer is not specified as packing bits in any particular format... if the a developer or end user requires a specific format, then they are free to implement their own within the standard. If you've come up with an alternative and you think it'd be useful, please post it!
That said, while the format/structure of the bits isn't specified, the LRM is very clear about how packers behave... it seems that the behavior just isn't exactly what you