We are making a siyum on Seder Moed and are finishing with the Mishna in Shabbos. I am writing a P'shetel attempting to address the Kasha as to why Abba Shaul needed to measure the barrel, since the Mishna in Oholos implies that only the tuma C'neged the tefach al tefach opening will pass out. Thus in the case of the Mishna, a complete meis will be lying in the alley under the barrel, only part of the tuma will escape, so WHY SHOULLD THEY BE MEASURING AT ALL?
The Meiri, who I am working on understanding and the Marsha's version of Rashi support problems with the Mishna, but I need more on the concept of Tuma escaping through the opeing and how it works?
One question, can we use the reverse concept of Shade greater than sun we learn in Succah (just like we use Lavud only for a coolah in tohoros?) i.e., the whole corpse tuma narrows to fit the opening just like the sun's rays expand through small openings? Thanks so much for your thoughts.
The Meiri gives two possible solutions to the problem you have raised. One, which he calls strange, is that the Tum'ah was indeed a small amount of Tum'ah that was only opposite the opening. Another, which he finds more likely, is that our Mishnah is in fact not in accordance with Halachah regarding Tumah as it argues on the Mishnah in Oholos (10:1) you quoted above. (Maybe they used some sort of logic similar to what you were saying regarding Sukah, although there is clearly no source there to tell us that the Halachah should be the same.) It was only quoted here to provide accurate information regarding Hilchos Shabbos.
The concept you mentioned seems quite simple according to the Rambam's interpretation of the Mishnah in Oholos (10:1, see Pirush ha'Mishnayos), who states that what is under the rest of the Ohel is Tahor because "the Tum'ah is not under the Ohel." A similar statement is said by Tosfos on our Gemara (DH "Hilkiti"), who also asks your question on Rashi.