Look at the letters that the sender sends. All the letters from A to H are sent.
Look at the letters that the receiver pays attention to. Only A, C, G, and E cause the receiver to do anything. In many cases, any letter other than A, C, G, and E causes stuff to stop happening.
What you really need to do, I think, is to send only when there is a transition on the sender. If a switch is pressed now, but was not before, send a letter. When a switch is released now, but was not before, send the other letter in the pair. This will dramatically cut down on the volume of data sent.