Iphone 5s reception

Hey guys so I noticed something with the iphone 5s.

I talk on the phone a lot with my girlfriend when we're apart, and she kept complaining that sometimes i sounded far away. Recently i diagnosed that it happens when I cover the back of the phone, ie when i hold the phone between my ear and shoulder, or when im laying down with the phone between my pillow and my ear. I thought it was because i recently switched to tmobile, and blamed them for crappy service. So I had her try it out, she has AT&T, and the same thing happens, she sounds like she's 10ft away.

Has anyone else observed this? Or can anyone else test this out? It really sucks that i can't hold the phone between my shoulder and ear without making it difficult for the person on the other end to hear me.

PS: unrelated but i noticed an interesting glitch in ios, try adding a favorite contact with multiple numbers, pick a number and when it adds the fav, it picked the wrong number. You literally have to pick the wrong number for it to get the one you want.