Adjust your machine and run 4 (or more) full-size strips with standard nozzle. Hopefully you will land at intensity of 12 (using 10% rule). Keep adjusting air pressure until your graph shows intensity of 12. Then, blast your shaded strip at the T1 time derived from this test.
Re-adjust the machine until you are at the 16 intensity (again using 4 or more strips and the 10% rule). Then, blast your shaded strip at the T1 time found from that test. The arc heights of the shaded strip are now the boundry conditions for your production runs.
Lance peening and shaded strips are challenging (difficult). Let me know if you need more help. You might also check out this article by Bill Barker from Progressive Surface:
http://www.shotpeener.com/learning/hole.pdf
