Welcome to the forum and welcome to this thread.
As mentioned previously in this thread, my instructions also say to mount the bung at least 18" from the port, but it goes on to say "if you expect EGT over 800 C". I'm still thinking that less than 18 is ok if Ducati can do it. Farther from the tail pipe would be good in my case because I'm using a relatively short reverse cone setup.
Can't say I'm in the mood to buy another (EGT) gauge after my recent fiasco with "Smiths" or should I say "the Smiths"..as in plural.
You probably don't want to drill a lot of holes in your exhaust header, but maybe you could take a length of 1 5/8" OD x 18" exhaust pipe (straight if possible, or with a bend if needed) to use as a stationary EGT testing pipe. You will have to buy an EGT meter (as cheap as $17 US on eBay) for measurement. If you don't weld, make a series of shallow cuts to form tabs around the end of the pipe fitting into the head. Bend the tabs outward to make a shallow flange for the exhaust nut. When you have the flange fitting into the exhaust port and secured with the nut, start from the furthest away part of the tube, drill a hole for the EGT probe, determine exhaust temp there, and continue the process, making new holes a few inches apart and higher each time until you get a reading of 800 C (1472* F) or higher. You can position your O2 sensor below that point on your actual exhaust header.