Berachos 13b Sugya d'Prakdan Lo Yikra Kriyas Shema - Part V

Continued from previous post...
Now, let's try to answer the contradiction in the Rambam. (It may be helpful to review the source here.) The easiest Rambam to deal with is the one in Hilchos Deios which forbids sleeping both on the face, and on the back. We can say that the Rambam is not saying this from a halachic standpoint, but from a health standpoint. The proof for this is, that if this was halachically mandated the Rambam should have said the clear exception - sleeping on one's face or back while tilted slightly to one side which is clearly permitted by the gemara in Berachos 13b. In this we would be arguing with the Pri Chadash and the Aleh L'Trufah who cite the aforementioned gemara on this Rambam, indicating that they read the Rambam as sourced from that gemara.
So, the Rambam in Hilchos Deios is not germane to the discussion of the meaning of the word prakdan. So what does prakdan mean according to the Rambam? (Noting that we have the contradiction from the Rambam in Hilchos Kriyas Shema to the Rambam in Hilchos Issurei Biah.)
It seems to me that the Rambam held that prakdan means lying on one's back. In this he holds like the first opinion that Rabbeinu Chananel brings down, Rashi and the Baalei Tosafos. That's the reason why in Hilchos Issurei Biah he only forbids sleeping on one's back - because that's all the gemara is talking about. And the gemara is only talking about lying on one's back because the subject is a chashash of hotzo'as zerah l'vatoloh, and for that there is only a problem on one's back.
However, in Hilchos Kriyas Shema the Rambam forbids saying the Shema both lying on one's face or lying on one's back. Why? Because the Rambam held that although the gemara only discusses lying on one's back, however, the reason for this halacha (because it is forbidden to recite the Shema while posed in a disrespectful manner) also applies to someone who is lying on his face. The Rambam held that too to be a disrespectful manner - derech srarah v'gaava (Rashi) - inappropriate for one accepting the dominion of Hashem upon himself. (Note that the reason of kishuy doesn't apply at all  when reciting the Shema - Maharsha in Niddah.)
This is arguing on the Beis Yosef and Prisha who said that the Rambam held that prakdan has both meanings, and arguing on the Biur HaGra who said that the Rambam was being machmir like both meanings. ומי אני לבא אחר הני מלכי -רבנן איקרי מלכים - אבל מה אעשה כשיש קושיא עצומה כזו ואין פותר אותו?
Coming next: A proof to this exposition of the Rambam's shitah from the words of the Tur.
To be continued...