A couple of things,
1) You've been beating this issue to death for answers for months now and you've gotten a lot to choose from, they are all random... decide what's right for yourself and move on. (in fact, of your 18 posts on the immigration website, 15 have to do with this issue. it makes me curious as to know why you never posted at all regarding any issue in getting your green card, after all that is were most of the hand wringing from people is especially in light of the retrogression issue... strange to say the least)
2) The reason they are all random is each one is not based on fact, but on each person's opinion or "feeling". You know what they say, "opinions are like assholes, everyone has one". As they are opinions, they are pretty much useless. So back to point 1, move on, as you are getting information that is not based on fact and is worthless.
3) The reason no one has a solid answer, is because there is NO specific requirement from the government. Nothing, nada. Go back again and read the requirements for citizenship... on their website, read "am I eligible?" You won't find anything and no reason to deny you. (now before I hear the protests about fraudulent getting of green card from people, show me the rule/regulation/guideline.)
4) JoeF who used to like to write here and admire his own self importance, hell the guy in 2 years wrote more than 10,0000 posts, can you imagine what value his employers got from his salary? Well dear old JoeF who set himself up as the all knowing immigration guru and would fight, name call, berate anyone who didn't agree with him would constantly state "6 month rule of thumb" as if it were law. In fact he stated it so much, people on this board would repeat the term so much so it was taken for granted there was a "6 month rule of thumb". Others who would intelligently question the validity, not the logic, in such a rule would call it "6 month rule of dumb". Essentially, because there is no ruling and no one knows, people throw up a time value like 6 months...feeling in their own estimation that this is a prudent timeline. Others will say 1 year, others 3 months, others 1 month and some 2 years etc.
5) To remove all the emotions from the discussion, we did a poll of people who went to their citizenship interview and asked if their employment history and length of stay after receiving the green card was inquired on. Of the approx 100 people who chose to answer the poll, none had. Now there were people that said they "heard" of someone but when questioned for specifics they had none. So you have to treat "hearsay" like a court would... they throw it out. Aditionally, the one post described in a previous post, the junior IO took it to her supervisor who approved it within 10 minutes. Now why was it flagged, maybe a nervous wife worded it wrong, maybe not. However the key wording here is they have to prove "intent" to defraud. Intent is a very very difficult thing to prove especially with all the variables in employment relationships, hence the rationale behind AC21.
6) Conclusion. Stop stressing, enjoy your life and do what's right for you. If that means changing jobs, do it. There is no specific rule. Do a poll here if it makes you feel happy.