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

Continued from previous post...
The Tur in Orach Chaim 63 (quoted previously here) says: וקורא אותה בין מהלך בין עומד בין יושב חוץ מפרקדן פירוש ששוכב על גבו והרמב’’ם ז’’ל כתב בין שפניו למעלה או פניו טוחות בקרקע לא יקרא ואפילו אינו ממש על גביו אלא מוטה על צדו לא יקרא מפני שנראה כמקבל עול מלכות שמים דרך גאוה. Look closely: First he says that one can recite the Shema any way except for prakdan, which is lying on one's back. Then he says that the Rambam says that whether one is lying on his back, or on his face - he shouldn't recite the Shema. He continues, that even if one is tilted a bit to one side he shouldn't recite the Shema. All this was from the Rambam. Then, he finishes off by saying that to recite the Shema in this way is forbidden because it looks like he is accepting the yoke of Heaven upon himself in a haughty manner. The Rambam did not say this.
Now, if the Tur is saying that the Rambam is arguing on the definition of prakdan - he should have written: One can recite the Shema any way except for prakdan, which is lying on one's back.  The Rambam says that whether one is lying on his back, or on his face - it is called lying prakdan.
If the Tur would have written it this way, it would have been apparent that he felt that the Rambam was disagreeing with the definition of prakdan that the Tur had just written, and therefore one would not be allowed to recite the Shema lying on one's face. From the way he does write it ("The Rambam says that whether one is lying on his back, or on his face - he shouldn't recite the Shema") - we see that the Tur understood that the Rambam also held that the word prakdan only means lying on one's back - not on one's face. So that raises a problem - why then, does the Rambam say that one should not recite the Shema lying on his face? Because of this question the Tur explains the Rambam by finishing off and saying that to recite the Shema in this way is forbidden because it looks like he is accepting the yoke of Heaven upon himself in a haughty manner. This is exactly like we explained the shita of the Rambam - that even though prakdan by definition only refers to lying on one's back, still, one may not recite the Shema lying on one's face because it is disrespectful. 
Coming next: Based on all the above, what is p'shat in the Mishne B'rurah?
To be continued...