Doesn't work for immigrants -- language (or is it cultural?) barrier, even a tiny one, makes face-to-face feedback to be accepted way too negatively, because those subtle tone hints are really hard to master.
In that case I would start by explaining very clearly that is the intensity of the words to be used, whether they express low/medium/high scale. And I would also explain even more clearly what's the level of intensity for me, so that the person understands what is at stake. In fact, I do it even with native speakers, clarity is godsend.