Unraid doesn't use ANY of the options shown at that calculator link. It's UNRAID.
As long as all the remaining data drives are functioning 100%, Unraid can emulate and rebuild from ANY number of data drives. It's currently limited by choice to 28 data disks, so if you have all the same size disks you have less than 3% lost overhead. The probabilities of one of the remaining drives acting up during a rebuild is not negligible, so we usually recommend 2 parity drives any time you have more than 10 or so data disks, but it's all a matter of statistics, and you can choose to run all 28 disks with one parity if you like.