Birchas Hamapil

In this post Chaim B. asks the following question regarding Birchas Hamapil:

The Rosh writes that the reason a bracha is not recited over sleeping in the sukkah is because there is always the chance that one will not be able to fall asleep, rendering the bracha l’vatalah. By the same logic, asks the M.C., how can we say a bracha of hamapil – why is there no concern that one will recite the bracha and not be able to fall asleep?

Rabbi Ehrman in this post also discusses the bracha of Hamapil and says as follows:

Yoni is a good boy! He is in Yeshiva and learning WELL!! He is giving his parents a lot of nachas. One night Yoni said the bracha of Hamapil and krias shema al hamitah before he turned off the lights and was ready to fall into a deep sweet slumber.All of the sudden he hears Avraham Fried belting out a niggun. His cellphone is ringing! Uh oh. He looks at caller ID and discovers that it's Mom. Holy beloved Mom. But after Hamapil and Shema he may no longer talk. On the other hand to answer would be Kibbud Aim. Question: May he answer?Answer: Answer! [See Shu"t Be'er Moshe 1/63] Note: One may also say Asher Yatzar if he relieved himself after Hamapil.

I actually looked up this Be'er Moshe and I found that he not only discusses Rabbi Ehrman's question, but he answers Chaim B.'s as well... with the same logic.

Basically, the Be'er Moshe holds (unlike the Mishna Berurah) that there is really no inyan to not make a hefsek between the bracha of Hamapil and sleeping. The only real reason to be quiet after Krias Shma Al Hamitah is in order to fall asleep "mitoch divrei torah". As far as Hamapil is concerned, it's not a bracha on the actual act of sleeping at all, but rather just a bracha on the "concept" of sleep. (He compares the bracha to HaNosen LaSechvi Binah.) Because the bracha is not on the act of sleeping, there is no worry of hefsek between the bracha and the act of falling asleep.

With this understanding, the Be'er Moshe explains the difference between Sukkah and HaMapil. By Sukkah, if there would be a bracha on sleeping in the Sukkah it would be on the act of sleep. Thus, the concern for bracha l'vatalah. By Hamapil, since the bracha is not on the act of sleep, there is no such concern.