I can't find the profile setting your are describing.
I did find this setting:
"Show most recent posts at the top." (with a checkbox)
...but that's NOT what I want to do. I like the format of oldest message at the top, most recent message at the bottom. It's just that when I click a thread, I like to be taken to the topmost OLDEST message, not the bottom-most recent message, because most times I want to read through the whole thread to catch up. If I wanted the most recent message, I would have clicked the little icon on the main screen that would have taken me there.