Your setting of +18 for volume is my normal listening level for broadcast TV. When watching a Blu-Ray this usually increases to 25-30 depending on the movie. The surround effects seem to increase as your volume goes up.
Remember in a theater you seldom, if ever, hear sound from behind you. People tend to want to increase this effect with their home systems. If you pay for it, you want to hear it. If you ever hear a correctly calibrated THX system, you will never notice the surround channels or the sub-woofer. Until you turn them off. If they are loud enough to be noticed, they are too loud.