Edwin; I thought about your comment on mixing your in-ears so that each instrument is heard relative to where you are standing on the stage. So I'm wondering if it's disorienting if you've been standing relatively still and then suddenly turn around to face your amp; or maybe walk over to face the drummer?
Before in-ears, if a player turned to face his amp, the brain would automatically compensate so that the other players were still perceived to be in their original relative positions.
Another example; if you're cooking veggies in the wok, you can turn and walk over to the refrigerator, then turn and walk over to the dining table, then turn again and return to the stove, and the brain automatically maintains the fixed location of the sound of the veggies despite the movement of the ears relative to the stove.
So, when you're wearing in-ears that have a stereo mix with the other players in fixed positions relative to where you normally stand on the stage, if you turn and/or move from that location, does the brain try to compensate? Or does the guitar player sound like he's suddenly on the other end of the stage, and the singer is out in the audience?