Kefiyas Hamita

The gemara on 27a states that it is not sufficient for the avel to turn his bed over, but all of the beds in the house need to be turned over. The clear implication of the gemara is that kefiyas hamita is not a din in the avel, but in the beis ha'avel. The rishonim debate whether the beds of guests should be turned over (see Rosh #78). Furthermore, the Rosh holds that one who did not turn his bed over but did not sleep on it either (he slept on the floor) has violated this halacha, further implying that this is a din in the house and not in the avel himself. If he did kefiyas hamita and did not sleep on it , he has fulfilled his obligation. The Rosh continues to discuss why we don't do this anymore (see also Beis Yosef who suggests that we should at least turn over our blankets and pillows). This, of course, is not the only example of a din in the beis ha'avel rather than in the avel himself. There seems to be two dinim in talmud torah - an issur ont he avel to learn and an issur in the beis ha'avel (see שולחן ערוך סימן שמד שאין אומרים שמועה ואגדה בבית האבל וכן נקטינן דלא כרבי חנינא בן גמליאל - ועיין ברש"ש לקמן למה לא אמרינן הלכה כדברי המיקל באבל).
The Chasam Sofer famously suggested that our minhag to cover the mirrors is based in kefiyas hamita because the mirrors are where we find the expression of our tzelem elokim. Along similar lines, Rav Hershel Schachter shlit"a has suggested that photographs should also be covered in the beis ha'avel because they also represent the tzelem elokim. (I heard he did this during his recent shiva - when I visited on Shushan Purim his pictures were exposed)