CentOS - Jun 2017 - how to enforce sunit and swidth for root device/partition when installing?

Hi,

how can I force the Centos 7 installer to use the particular
sunit and swidth values that are matching the hardware raid
device I?m installing on?

The installer forces me to reformat the partition I want to
install on :(  It does not let me specify any options about
creating the file system :(

Even when I create the file system manually with correct values
after telling the installer where to install and before beginning
the installation, xfs_info shows different values for the file
system than I used when I created it once I rebooted.  So apparently
the installer re-creates the file system again when I start the
installation after it had me accept the changes it wants to make.