Googling around, I'm finding rules of thumb that say a tenon's length should be 5x its thickness, and the thickness should be 1/3 the width of the piece it's going into. But for joining two 4x4s (3 1/2" x 3 1/2"), the thickness is 1 3/16", and 5 times that is...well, *a lot*: basically 6 inches. That's straight through the 4x4, that doesn't make sense. But my tenons are really short. Is this going to be a problem? How is this supposed to work?