Where in my cross-posted question should I mention that the question is cross-posted?

Question

What I understand about cross-posting: Usually, don't. But whenever you do (like if it's really justified to do so), then mention it.

Ok, assuming for the sake of argument that something is allowed to be and is cross-posted: Where in the post do I mention that it is cross-posted?

1. At the top of the post (before people have a chance to choose to read something that is cross-posted)?
2. At the bottom of the post (after people may have already read the post, and have probably even made some notes in an effort to answer the question)?
3. Other?

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Context: I was told Choice 2 here: Is there anything to improve in this post which is about ambiguity in question about field axioms?

An idea: Reddit does sometimes both top and bottom and sometimes just bottom. Not so familiar with reddit but if you use the 'crosspost' button then you can see both top and bottom. But I've seen people post the same thing without using the crosspost button and it ends up just bottom. (Not sure if reddit allows that but they do find out about the crosspost without the button because you see it at the bottom ultimately.)

Idk but from what I know: the reason why I was told to not cross-post (at least without mentioning it) is that people may waste time on 1 site when it's asked somewhere else. I mean even if the post isn't (or isn't anywhere near) an exact replica. If there are similarities, then it could still waste time if it's just at the end.

But whatever if it's better to put at the bottom, then ok. But I don't want to waste time of anyone who's/who would be/who would have been generously helping me, and I also don't want to be criticsed/judged by people in the future like: "Hey why did you mention the cross-post only at the bottom? Why are you wasting time of people who are generously helping you?" In this case, I want to be able to link to this and be justified in putting cross-post notices at the bottom to defend myself from criticism/judgement.

Answer 1

I recommend never cross-posting a question by simply copy/pasting it from one site to another. If that is what you want to do, then I think you should delete it from the original site, and re-ask it as a new question on the new site.

If you are not copy/pasting, and instead are writing a new question on a new site that in some way relates to a question that you are leaving on its original site, then I would not consider that to be a cross-post. The way I recommend to reference it is by writing somewhere in your new and old question bodies something like:

This question relates to a question that I posted on SITE_X as https:SITE_Y/stackexchange.com/questions/YOUR_QUESTION_NUMBER but it is not the same question because here I am asking ... whereas there I am asking ...

I think it will usually be best to provide this context to your question at or near the beginning of its body but there may be occasions when, for readability, it is better to mention it further down.

Answer 2

Cross-posting, in the strict sense of copy-pasting, is generally discouraged.

However, if your question is based on a fundamental aspect and you want to post two substantially different variations that make them related but distinct, and are on-topic on different sites and the linked question adds relevance to the overall context, then I would choose choice 1:

at the top of the post (before people have a chance to choose to read something that is cross posted)

However, in case the linked question and its answers do not substantially add to the context, then it can be taken as a sort of footnote, as described in choice 2

at the bottom of the post (after people may have already read the post and have probably even made some notes in an effort to answer the question)