I think you have to see what #s he gives you. If PSs above 150 aren't giving you good nadirs and you want to consider a lower no-shoot, then you evaluate your data at that point and decide if a lower no-shoot is warranted. Most cats that I've seen on PZI will get a good nadir off a 150 PS, that, and safety reasons, are why I don't like lower no-shoots unless you have a cat who has proved they are needed.
That said, when I say 150 no shoot, I mean you retest and then shoot, I don't mean skipping a shot. If you see something like a 130 in the morning and retesting isn't possible, then I'd shoot a token dose like maybe 0.2 to give him something to get through the day and ensure you'll have a shootable PS in the PM. Then in the PM you reduce the dose from what you gave the night before so you'll get a shootable PS the next morning.
The ideal IMO is to get consistent PSs around 150 - 180. If you get a PS higher than that it suggests your dose is too low, so you fatten it up to aim for a 150 next time. If you get a PS below 150, you skinny up the dose so you can stay on track. And then you test periodic nadirs to be sure you are getting something in the 50 - 80ish range for nadirs. If the nadirs are lower than that then you need to lower the dose even if it means higher PSs. If the nadirs are higher than that, then you can reevaluate what you need to change as far as your PS (or possibly going longer than +12 between shots) to get the nadirs you want. Ideally with PZI those are the #s you will hit, and the 150 has a logic to it in terms of % drop to a nadir. Of course ECID though, but to me that's your starting point, and if your cat doesn't hit the 150/60 pattern, then you reevaluate your strategy.
Just my take.

PZI is so flexible, you can work it lots of ways. If you are hoping for OTJ, then the more hours he spends in mid to upper greens, the better. If you want to keep him regulated but are less focused on OTJ, then you try to keep the #s consistently in the blues & greens, or maybe under 180.