Ok, I see what you are saying about flow vs pressure. The common nomenclature used is "drive pressure", which to most of us encompasses exhaust flow and pressure. Because what we measure is the drive pressure. So opening a gate dumps flow/volume, which in turn drops pressure. So thanks for splitting those hairs for me. From my real world experience, I have seen plenty of engines get "choked" by too small of turbines restricting flow from the engine at higher RPM causing a drop off in performance. I'm not saying you are wrong, I am saying gating around the secondary turbo has been proven to work. I am not wanting to drive the primary with the majority of the compression. What I would be looking to do is monitor drive pressure in the exhaust manifold and tune accordingly. Here's an example of what I am saying:
"Truck #1- 1996 Dodge Ram, minor fueling upgrades, 57mm/71mm ATS compound turbos with a single internal wastegate, street truck.
We had the pleasure of tuning this truck on the dyno with pressure monitors everywhere, so we can report on how much power it made under various configurations. Before we hit the dyno, we ran it on the street where it only made 57psi with its limited fueling. That seemed low so we pinched off the wastegate line, effectively closing it. Boost hit 65psi, but the truck didn’t feel any faster.
The dyno would tell the story. After our first run, the truck made 400rwhp at 65psi, but with a whopping 99psi of backpressure (or drive pressure) which was far and away from the magical 1:1 boost to drive pressure that most folks aim for. Opening the wastegate saw a drop in boost of 8psi to 57psi, but drive pressure was a mild 64psi, and the truck actually picked up in power to 432rwhp! In this case, wastegating netted an increase in power even at a lower boost level, due to an increase in engine efficiency."
I'm quite certain your calculations are correct and using them to size turbos works. But so does known procedures based on experience, and even well planned out and pressure ratio matched turbo setups require tuning and are directly impacted by individual performance requirements. So in a controlled environment where the variables are controlled to fit within the parameters of the calculations, I'm sure they are great. But if it was mine, I would still tune the setup to the engine in the vehicle in which it will be used, so all the variables are applied and I can find the best performance compromise. That's how I do it, and so far it's worked well for me.