If it’s stereo, why do I hear it behind me?

It’s actually a psychoacoustic phenomenon. Some of the acoustics, though not all of them, from the original recording session, made their way onto the disc, into the player, out the speaker, and into your ears. These are cues like difference (L-R), frequency spread, delay, and echo. In some cases, you may even be able to hear sound as if it’s bouncing off an imaginary ceiling. “But it’s only coming from two speakers!” Well? You only have two ears, not 5.1 ears!☺