I've noticed my Custom Black sounds a little bassier when I'm sitting up. When I lay back it sounds more balanced. Most time I liten to my music while laying back so it kinda works out. It never feels like its going to fall out though. Has anyone experienced this with a custom?
The human ear can slightly change its shape depending on the position of your head, your jaw, etc., so this is very much natural. It's why an IEM can also sound different or fit differently when we're eating, yawning, etc. You lying down may have caused a slight change in shape that's allowed the slightest loss of a seal, which reduces the bass response.