So, I've always been struggling with E shape barre chords and i've always found ways to avoid them or to "cheat" (playing them like Hendrix with the thumb over the neck or not pressing my index finger on the strings that are already fretted by other fingers). I want to learn to barre properly, though. I can't do an E7 shape barre chord if I'm unable to press down on all the strings with just my index finger.
Actually, I'm almost able to do it. My problem is that the B string falls right into a crease on my finger and it doesn't completely ring out (it buzzes a little). If I press down really hard, I can make it ring out but it also makes me press down too much on the other strings, so much that the G string goes slightly sharp (on an electric, no wound G).
I'm also wondering if I place my thumb properly. Here's a picture:

From what I've read here and there, my thumb should be more to the left, just below my index, right? When I place my thumb the way it is on the picture above, I also tend to stick my arm against my body, and it's probably not a good idea.
I tried something else today:

It certainly looks better, my arm isn't stuck to my body, but as soon as I try to place the other fingers, the B string doesn't ring out anymore, unless I press really hard and the G string goes sharp, just like I said.
Does anybody have any advice? Can you confirm that the second picture is right regarding thumb position?
Thanks!