The concept to "get" here is that negatives typically catch a lot more of the scene (shadow and highlight) than gets used to make a print.
Your 2/3's over/under test isn't a big enough swing to bump TX's limits, it would typically be quite easy to make good prints, with the detail expected, that look essentially the same from all three exposures. This does depend on subject matter and personal prefs but given your comments I doubt I'm wrong.
I'd suggest shooting a single roll of a single subject with a mid-tone reference (a face or gray card or...) under unchanging light starting at maybe 4 stops under and bumping up in 1-stop increments to 5 stops over, 10 shots total. Develop normally then print "to the mid tone" so that the mid tone matches in all ten prints.