Calamares won't just replace a partition

[D0glover]

Good afternoon. Thanks for Sparky.
I cannot get Calamares to just replace a partition, which is one of the choices.
The partition is already created, 25GB. There is also a swap partition already created.
When I select the 25 GB partition, instead of just replacing it, it wants to create a lot of free space in front of it and shrink the partition behind it.
Anybody else have this problem? Most of the distributions I install don't use Calamares, so am less familiar with it.
Thanks, best
IMF