The distance is not all that important, but if you want to compare readings with your buddies, put it where they have it. On my Yamaha I always put it 3 1/2 inches from the piston face, with the tip in the center of the tube. The only thing you're really need to worried about is getting the highest readings possible. Both low-end and high-end, they will be different. If you go too high, the engine will start detonating, and the EGT will read lower. Don't be fooled. And don't get the idea that the EGT reads higher the more RPM you turn. When you're coming off the corner, with the clutch slipping, because that's where the pipe is working the best, and creating peak torque, you have to run a lower EGT to compensate for the increased heat and/or pressure. The EGT has a very quick response time, one or 2 seconds, maybe less. It gets hotter on the top end because the pipe becomes less efficient creating less heat and/or pressure, so you can run leaner. Never look for one fixed peak temperature. It will vary, depending on air density, fuel used and other things.