Relocate the antenna that comes out of the box under the rear seat, and thread it up the back of the rear fold down seat. Between the carpeted backing and the seat cushion material. Then across the top a tiny bit so it forms an inverted L shape. The antenna is BLACK and is only attached on one end to the remote locking module.

What does this do.... Gives a HUGE range on what was previously believed to be a shitty remote. Its not the parts.... its the poor installation of them. That antenna is used for Frequency Modulation reception, FM is line of site, Line of site doesn't mean Superman's X-ray vision, RF signals don't travel through sheet metal too well. So the antenna being under the rear seat, and atop the gas tank and behind the trunk lid and doors, DOESN'T HELP.

This problem has bothered me for so damn long and I am so happy I fixed it. 

Later cars have the remote locking module integrated into their locking pump which resides in the foam casing in the trunk. Certain years had a technical bulletin applicable on how to use a kit (new antenna) supplied by Audi to increase the range. There may be a way to modify the later cars... however I have yet to experiment with them.