Good. Then until you ask, you start with the most basic form of the label.
I don't assume you're a positive atheist, but I also don't assume you're a negative atheist. I'll expand on this below.
A lack of belief in god or gods is the default though. All of atheism starts there. Specific atheists can add more into their views beyond that, but that's not the default. Similarly, the default theist is someone who believes in a god or gods. The default theist is not a Hindu, a Christian, or a Norse polytheist.
General first (default), then specific. You seem to want to start with the specific first and I can't determine why. You shouldn't make that leap before you are certain.
I have no idea where you got the impression that I want to start with any particular specific definition as I explicitly stated that we ought to avoid ambiguous words (or words which other people participating in the conversation find ambiguous) and instead use a more precise and transparent definition if possible.
It could be granted for the sake of the argument that all of atheism starts with the lack of belief in God (then you would run into problems such as agnosticism becoming a type of atheism as well, despite the historical insistence of agnostics not to be labeled as atheists even in the negative sense), but I just don't think the default meaning of words should be decided by picking the one meaning that holds least information content.
Definitions are, in my view at least, a matter of practicality. If most people agreed that atheism meant a mere lack of belief in gods and took it as obvious, then I'd have no problem with the term "negative atheism" being considered unnecessary. I do not think, though, that this is at all the case. It certainly isn't the case with the OP who is asking if atheism is restricted to the negative sense (that's my takeaway) so insisting on calling negative atheism simply atheism and avoiding to bring up the distinction when it is needed is highly misleading, if not downright deceptive.
Theists tend to talk about atheism that way, and they are often mistaken. What these theists are actually pointing fingers at is things like antitheism while mistaking the labels entirely. You just need to learn to separate your labels more. Just because a person has two labels does not mean the two labels are equal or always tied together universally.
It is telling that you assume this is just something the theists do. Even more uncharitable is your claim that this is a product of the theists' confusion of atheism with anti-theism. What I was referring to in that paragraph was actual academic discourse on this subject. Take the article on atheism in the Internet Encyclopedia of Philosophy whose author is an atheist:
"Atheism is the view that there is no God. Unless otherwise noted, this article will use the term “God” to describe the divine entity that is a central tenet of the major monotheistic religious traditions--Christianity, Islam, and Judaism." [1]
In one paragraph he does both things I talked about. He also writes against negative atheism in his other work, which shows that positive atheism is not necessarily just negative atheism with some additional arguments against God. Here's the article on atheism from Stanford Encyclopedia of Philosophy:
"This requires examining the surprisingly contentious issue of how best to define the terms “atheism” and “agnosticism”." [2]
After some discussion on how the terms atheism and theism relate to one another, the author says:
"Therefore, in philosophy at least, atheism should be construed as the proposition that God does not exist (or, more broadly, the proposition that there are no gods)." [3]
This article was written by another prominent atheist scholar Paul Draper. These were just two examples of atheist scholars who specialize in the field of philosophy of religion who not only don't think the term atheist is negative by default, but they downright say the positive meaning should be preferred. I was being quite charitable in trying to find a compromise and I'm a Christian, so no, this isn't the issue of me needing to learn to separate labels (that was never an issue to begin with as it is actually you who wishes to collapse two labels together while I'm advocating for a clear distinction).