To make this simple, when BE is involved, all BE rules apply unless UA has specified an exception. So when BE does not deserve a seat assignment, no advance E+ for BE.

But because how seats are assigned, a BE customer may be lucky enough to get a E+ assignment. But again - they can't be switched because it is BE (again).

So the chance of your companion sitting next to you is extremely slim.

But again - this is moot because you are only a Silver, as you may not even have E+ for yourself.