Arvus Or Shomea

The Shulchan Aruch (219:4) says אם בירך אחר ואמר בא"י אמ"ה אשר גמלך כל טוב וענה אמן יצא.  Rabbi Akiva Eger asks why does the person have to answer amen to fulfill his obligation if normally שומע כעונה does not require the one listening to answer amen to fulfill his obligation?  He gives a few answers.  One answer is that the principle of שומע כעונה only applies when hearing a statement from a בר חיובא as opposed to here where the one saying the beracha is not obligated to make a beracha.  R.A.E. says based upon this that וא"כ בכל ברכות המצות דקיי"ל אם יצא מוציא מ"מ כיון דאין המברך מחוייב עתה בברכה זו לא יצא בה בלא עניית אמן.  We see from R.A.E. that he holds that the principle of  ערבות works with the principle of שומע כעונה.  Arvus merely extends the principle of שומע כעונה to say that even one who is no longer obligated and normally wouldn't be able to say a beracha for someone else, due to arvus they can.  This is not like Rav Leeb Malin siman 5 who says that the principle of arvus is separate than that of שומע כעונה.  He says שומע כעונה means that when a person says a beracha it's as if the one that needs to say the beracha said it himself.  However, the principle of arvus says that one person can say a beracha for someone else and there is no need for  שומע כעונה.  Nonetheless, he does arrive at the same conclusion as R.A.E. that in order to be yotzeh a beracha through arvus one would need to answer amen in order for the other person's beracha to work for the recipient.