I also use the Tandy Pro Groover and an old Rampart groover. What I have found is that I had to strop or polish my cutting tip right out of the bag. This will help you 90% of the time. The rest of Art's advice will get you there. As for the distance, what I was taught was that I use the thickness of the compiled leather to determine the distance, but do not exceed more than 3/8' from the edge. I say this because some makers use really thick leather like my two pancake holster that I made some years back around the belt slots for reinforcement.
A couple more tricks or tips if I made impart on you (from lessons learned), if you happen to stitch too close to your edge and you notice 'bumps' or 'lumps' on your edges especially when you finish them. Your distance my be off or too close to the edge so be careful when guiding your distance. Finally, when I start my groover, unless I have practice on scrap (highly recommended), I would take a light pass to start off. Once you get the feel (or warm up to the tool) you can readjust the pressure and go for it.
Good luck and Happy carving stitching!