The reply button is intentionally at the bottom of the topic. The idea is that one would read the other posts in the topic first before replying in order to reduce duplication of thoughts and let others be heard. That said, you can simply tap the right half of the topic progress meter at the bottom right to move instantly to the bottom of the topic. And of course if you are replying to a particular post in the topic, tap the reply button on that post itself.
You can also hide the editor preview by tapping the hide link in the lower right of the editor, when the editor is visible. This preference is saved in your browser’s local storage.
