Okay. It could be that it by default are looking for the time property and sorting by that.
Please note that you can sort a table on the client as well. So make sure that you sort the metrcis value in client descending.
When you done this, then save your dashboard. Next time you visit it, the sort should be persisted.
If this not is working out for you, please show me a screenshot of your metrics tab, options tab and column styles tab.
Marcus