Ubuntu packages are not relocatable. Their files goes wherever the package says they go. The same goes for most distributions.
When you have a packaging system, there's not much point in having relocatable packages. The package manager keeps track of where the files of each package are located, so they don't need to be grouped in any particular way. The system administrator doesn't need control over where each package goes: there's a location for files managed by the package manager, and the administrator does not manipulate those files directly, only through the package manager.
On Linux, the norm is to put programs managed by the package manager under
/sbin (plus a few more, I won't go into details). Programs installed by the system administrator without using the package manager go under
/opt. (Some distributions also put things under
/opt, but not Ubuntu.)
The distinction between
/bin and siblings and their counterparts under
/usr is that the things that are needed to get the system operational all need to be outside of
/usr. This distinction dates back from times when it was relatively common to make
/usr a separate partition: anything needed to get that partition mounted, or needed for the system administrator to log in and repair stuff, had to be outside of
/usr, directly on the root filesystem. These days, disks have gotten large enough that a network-mounted
/usr no longer makes sense in most setups, and filesystems have progressed so that mounting
/usr read-only no longer gives an advantage. So the distinction between
/bin-and-siblings is moot; some distributions (such as Ubuntu) preserve it, others don't (and make
/bin a symbolic link to
/usr/bin or vice versa).
The split between the root filesystem and
/usr is by file, not by package. Every Ubuntu package includes at least a couple of documentation files that go under
/usr/share/doc. Most packages that put files in
/bin also put files under
/usr, e.g. executables that are less critical, man pages, etc.