Well, it doesn't matter about the psi or the head or the coverage BECAUSE rachio assumes that the irrigation zone was installed properly which means that each zone is receiving a uniform distribution.
Now don't light into me yet, uniform cant always be achieved with with most geometries you find in yards. So obviously some areas in a zone get more or less, this is referred to as "efficiency". 100% efficient means a uniform distribution.
Now to really answer your question, when your system is designed and installed, the installer should be able to calculate your precipitation rate. "Pr" in the head setup of an app.
So, yes, psi, coverage and other things go into it, but all off that collapses under the pr. And if your efficiency is under 65%, I would recommend tossing your installer a 9mm salad (unless you didn't want to pay the premium for odd geometries).
So if you have a pr of 1.5 inches an hour, your soil type defines the volume of water the soil column can hold, so, at this point we know how much it can hold and how fast we apply it, the only missing variable is time, and that is determined my volume / pr = time. There is more that goes into it if you dig on the forums you can find a thread I was in that got too detailed.
now, the discussion of how you raise your zone efficiency when you have a zone mixed with 90/180/360 heads is another discussion, but psst, you have to change the nozzle on the heads to increase the 360 head flow rate and decrease th 180, and decrease the 90 even more.
That is really what you are paying for from the installer, the cheaper the installer, the less they think about the efficiency.