Jarek,
I do not say you are wrong, all the texts and good teachers say the same so it is perhaps better if we stick with with strict and precise location. But I am not so sure all those small deviations from strict description are necessarily wrong. (I do not know if you teach but many of my students have peculiar characteristics so I learned not to be overly strict, I do not think to say "this is the only way and all other is wrong" is useful. On the contrary, I often say "everything is correct, if you know what you are doing and why.). I do not know what is better - whether to be strict and tell the student "only this is correct, so wait until you get it" and they maybe will never get it, or to tell them "ok, try various possibilities and eventually you will find by yourself what is suitable to you". For now, I find second attitude to be more useful.
And also, when you do transformation Qi to Shen, cauldron moves up (stove stays there). That process of moving cauldron is not discountinuous so the feeling is that dantian loses its "fixed" (or strict) borderline, no? I do not know, it is hard to talk about this, it is much better to see it. Pity you are so far, next time you will go home, let me know, I would like to see you. And thanks for good discussion. Btw, could you write characters for Cao Xinyi or tell me something about him? I did searching his name in pinyin and did not find anything. Or even tell me about your conversation with 胡海牙, please. Thanks.