well you use the variable parts to see what matching actually does, then if you like it you figure out how to match it cheaply (i.e. parallel/series components)
How are you measuring performance of the device during match tuning? I suspect your IA will have a difficult time (not sure how well it can mimic a real Keysight IA).
You should be able to produce a graph of output power vs tuning some how
I do see values of nF for capacitor, but I don't know about series L. I only worked with one piezo device and I never finished the project.
Not sure if you want to say tuning/adjustment is bad for production, its best avoided.. but it might be unavoidable. Plenty of good profitable things get adjusted. You need to test products before sale typically, especially if they do a process (you can't just plug it into a card, you need to make sure the transducer works and is in spec), so having the test technician trim something is not outlandish.
I assume you will have to test a glue bond to the device being stimulated anyway. Don't pull a harbor freight and sell a ultra sonic cleaner which has the horn fall off and melt the chassis and try to light tables on fire..............