Dear Zev,

That is a good question. The Meiri says that the simple reading of the Sugiya is - like you say - that a Ba'al Keri only has to be Meharer when he is with the Tzibur but when he is by himself he does not have to, and this is, he says is the conclusion of the Gedolei haMefarshim (Ra'avad) and Geonei Sefarad (Ri Migash). But the Meiri himself is Mechadesh that even at home the Ba'al Keri should be Meharher - at least for Krias Shema - because Hee Sha'as Kabalas Yichudo LaKol. According to the Meiri it is not the place where the Tzibur is involved in a Mitzvah but the time.

Kol Tuv,

Yonasan

This is not a Psak Halachah