Disk imaging and restore question (again)

I may have mentioned this before, but I want to use a specific example to
make sure I have this down right:

C = 40 GB, D = 40 GB (and my C is almost full now)

I also have two backup images of each partition on another drive:
Let's call them bakC1 and bakD1 for the two respective image backups.

Let's say I now change my source drive to:
C = 50 GB, D = 30 GB (since my C was getting full)

Now if I understand this correctly, *if* I were to restore bakC1 (40 GB) for
some reason, there should be no problem, since the source drive has 50 GB
reserved for C now anyway (with 30 GB adjacent to that reserved for D).

BUT if I instead were to restore bakD1, there *would* be a huge problem
(since the first 50 GB on the source drive now stores C, and there is only a
30 GB adjacent physical segment left to accommodate the 40 GB. So my guess
is most imaging programs would fail at that attempt.

Note: Implicit in all of this is my assumption that normally when you
restore an image back to the source drive, nothing is relocated or moved on
the source drive to make room for this, which would be way too time
consuming. Rather, the original existing partition is simply marked as
deleted, and the new one takes its place in the same physical area of the
disk. (That way there is no time consuming relocation of any existing data
to make additional room for anything - like having to move any existing
partition data out of the way).

It may depend on the imaging program, but I'm guessing this is standard
practice.

Is this correct?