Is there a rule of thumb for the height of and end table? I am in the process of constructing a simple end table for next to the couch. Not sure on how high to make it. the top is 20" square, legs are 2x2. Should it be higher than the couch arm? lower? even? there will be a lamp on the table. There will be a small shelf near the bottom about 6-8" off the floor.