Right after a reboot, I run at like 20% memory usage...it's almost a full green bar for memory.
Opening an app immediately brings me down to near half...but still green, so more than half...
If I do a few more things, it drops to yellow, but still near half full...so I guess, I'm on the other side of a half (I guess 40% left?)
I've never seen it go as low as you suggest, but this is my personal experience.