I just tried that but it was impossible to do...I used this thread --- I logged out and viewed your post and changed to FLAT view...it immediately showed me the OLDEST 10 messages in this thread. I tried changing to NEWEST first and it immediately reverted to THREAD view. So I selected FLAT view again and it took me to the 10 oldest posts again. I tried expanding to show up to 50 messages per page and clicked and it reverted to THREAD view...so even logged out it was not possible to choose the settings I wanted --- they kept reverting to the default each time I clicked.
Personally I'd be happy if they just changed the default to NEWEST first and 50 per page and FLAT view. Then if it wanted to revert it would revert to my settings. I can't imagine anyone wanting only 10 messages per page with today's fast Internet connections and can't really imagine anyone wanting a default of THREAD view. Impossible to follow a thread in that view. And can't imagine anyone want to start always with the OLDEST on top.