I do not understand your question.
When I click Reply at the bottom right corner of a post, the Editor panel shows me that I am replying to that particular post.
If I click the blue Reply button at the very bottom of a thread, I am not replying to anyone or any post in particular.
I have also noticed that if I reply to a post and my reply would not be the immediately next post to it, then an indicator of X number of replies will appear in the bottom left corner of the post I am replying to. Is this effect what you are asking about?
It seems that if the immediately succeeding post is written reply to the last post, then there is no need to indicate that it is a reply. Because this fact is self-evident.
Now, when someone else down the stream also replies to the same post, then it makes sense to indicate there are replies to that particular post (including the one that immediately follows the post).