What type of chairs are you sitting in? If you measure your ear height on most couches or recliners for Home Theaters setups, it is pretty close to the 37.5" height. Besides, the tweeter sound comes in a cone shape into the room not directly at you.
Many people treat their side walls/ceilings with absorption material as the sound reflects off the walls/ceiling as well.
Now there is something to be said about trying to have your left/right main tweeters as close as possible to the Center, but that is not set in stone. You could always angle your center towards you.
