The reason I asked was that I too had problems at first trying to get ARC Virtual Control to work with using the rear port. It only would do so if the rear port was set to 115200. Even though communications took place if 4800 (the default) was selected, ARC Virtual Control and the scanner wouldn't talk to each other until I selected 115200 on the rear port. (But then I had to be sure to revert back to 4800 for GPS purposes).
Also if I used Sentinel's Profile Editor, I had to be sure the appropriate baud rate was set for what I wanted to do (either GPS or Virtual Control). I found that if I selected 115200 on the scanner, but later wrote to the scanner using Sentinel, the settings were changed. It took me a little looking, thinking and a bad word or two, to figure that Sentinel was still set for 4800 on the baud rate.
These are really neat scanners and software (Sentinel and ARC), but there are many settings that have to be "just so", otherwise things won't go as good as I hoped.