The Gemara asks why R. Yehuda is machshir if the person thinks about a) being zorek "inside" zerikah which should be "outside", and b) the reverse, being zorek "outside" zerikah that should be "inside". The answer is that R. Yehudah requires "meshulash", therefore the hechal ("inside") is excluded from "chutz limkomo". I see how this answers point a, but I don't see how this answers point b. After all, if he thinks about doing zerikah outside when he should be doing it inside, that "outside" is meshulash! Hope you can help.
Eliyahu Yaniger, Efrat, Israel
The Tosfos Yom Tov on the Mishnah asks your question and leaves it unanswered ("Tzarich Iyun").
However, Rebbi Akiva Eiger is perplexed by how the Tosfos Yom Tov could be bothered by such a question, because the Gemara is following the opinion that "she'Lo bi'Mekomo" is "k'Mekomo." That applies to the Mizbe'ach ha'Chitzon for Chata'os Penimiyos as well, in which case the Gemara never asked from the case of thinking about doing "outside" what belongs "inside," for in that case -- even if he actually went through with it -- the Korban would be Kosher, and consequently, as Rashi explains, the whole question was from the opposite case (of doing "inside" what belongs "outside").
See Insights to this Daf for more on this matter.