Programming the ATmega16u2 on an Arduino Uno R3

Hi everyone, I hope you can help me with the following issue.

I am trying to program the ATmega16u2 with new firmware by following this tutorial. However, in the section titled "Reset the 8u2 or 16u2", where you reset the ATmega16u2 and bring it to DFU mode, shorting the RST and GND pins on the broken out ICSP header (as shown on the picture) does nothing. Correspondingly, the dfu-programmer script does not detect the device (tested under both Linux and Windows), and the USB device continues to report itself as an Arduino even after the reset. Could anyone help me with troubleshooting as to why the ATmega16u2 would not reset?

Thank you for your help!

NB: Full disclosure, I have opened a similar thread here and received no responses in a week, most likely due to the wall of text that accompanied it. If this was wrong of me to do so, I'm happy to take this down; I reposted it just hoping to get some answers on an issue that has been bothering me for a while now.