When the "Quick Reply by default" option is checked in the "Composer" tab for an account, a Quick Reply window opens if replying to an email.

The window currently opens on top of the email you're replying to. It would be nice to open the window below the email instead, GMail-style. It would be less of a mental model change coming from GMail. If this is not possible for some reason, it would be great to at least have the option to do so.

My guess is that the Quick Reply window currently opens on top, because the Reply buttons are located at the top. If you had the option of keeping the Reply buttons at the bottom of an email, opening the Quick Reply window at the bottom would make a lot of sense.