I'm a big fan of sensitometer/test strips from step wedges contacted on film. I would go that route if flare-free testing was my aim. Though you are right, the suggested test of a single-tone target would be relatively flare-free.

There is no definition correlating density to a particular Zone, but this doesn't mean you can't use three arbitrary exposures to base a custom "test strip" upon. You can pick any two, three or more steps. Heck, you could do an impromptu test anywhere you go on the first roll of the day... Meter at f/5.6... Open to 2, shoot, stop down a stop, shoot, and quickly fire off 5 or more frames a stop apart.

Then when back from the day, develop that roll and see whether it's good for that camera/lighting conditions/day. If so, develop the rest of the rolls, if not tweak up or down a minute or two according to your preferences...