delete your old partition before installing using the restore utility on the install disk.
As I said earlier, I prefer to re-initialise my RAID array and perform a standard install as it is repeatable and documentable.
That said, I followed your advise and did not enter the "destination" section and the partioning is as it should be.
On all my previous SME-10 installs, the destiantion section was showing as an incomplete step, the same as is shown for date time & keyboard. Possibly because my RAID array way not empty?
I guess after 23 years of using the simpler installs from previous versions I am finding the new installer confusing and a little buggy. e.g. Often the install crashes at the select language page.