I can't believe I have to consult Motor Trend, but some tidbits:
https://www.motortrend.com/how-to/hrdp- ... -location/
Everything changes with really large injectors (over 96 lb/hr). High-capacity injectors generate a relatively poor spray pattern with a large fuel-droplet size. As Duttweiler puts it: "You're practically just spraying raw liquid. If you put a big injector too close to the valve, there's not enough time for the fuel to mix with the air." Large injectors would most likely be used in large-displacement or high-rpm engines with lumpy cams. High rpm translates into less time between injector firing pulses, lumpy cams generate poor vacuum, and the typically large-volume inlet runners needed to feed all those cubes generally mean lower air velocity downstairs. Obviously, all this adversely affects proper fuel atomization. Moving the injector farther away from the valve allows more time for the air/fuel to atomize properly and remain in suspension when air velocity comes up at high rpm. This should improve peak power but-because of poor low-rpm velocity-at the expense of idle quality (there's no free lunch).
Looking at some real-world examples, Strader reports that on a 1,000hp engine, the injectors were originally located 7 inches back from the valves. Doubling this distance to 14 inches was worth 50 hp on top, a 5 percent gain-but "it wouldn't idle below 1,600 rpm."
In the real world, mass-produced aftermarket cast-aluminum manifolds have the bosses added as an afterthought to a preexisting design. The placement is more for convenience than for best engineering practice-the available packaging architecture (including fuel-rail mounting and clearance) to a large extent dictates the nozzle location. A decent compromise for a hot-rod engine is to locate the nozzle about 1-2 inches upstream from the manifold flange to give atomization a chance, positioning the fuel rail at the best angle you can get away with and still package the harness and fuel rails. As Duttweiler puts it: "If you aim the injector more toward the valve, the fuel rail usually hits the plenum" on a converted classic V-8 carburetor-style intake. Note that at the OEM level, the trend on today's new-tech V-8 engine designs is to make them wider than a similar-displacement, old-school, classic engine. The included valve angle in some of the new late-models is nearly straight up and down in relation to the bore. That means the runners are also near vertical, which in turn allows mounting the injectors more vertically to provide room for the fuel rails and wiring harness while still maintaining a good intercept angle to the runner.
Circling back to Kenny's statement about those large injectors. I don't think anyone has really developed a high pressure system for something like that. F1 builders kept going higher than 100 bar and kept making more power, but rules eventually limited them. Now they use totally different designs.
You can read about Honda's F1 system here:
Development of High-Pressure Fuel Supply System for Formula One Engine
http://f1-forecast.com/pdf/F1-Files/Hon ... P2_15e.pdf
Important factors in boosting the performance of today’s Formula One engines include: the realization of the formation of ideal air-fuel mixtures and the achievement of greater combustion efficiency, through the use of shorter fuel injection periods and increased spray atomization resulting from higher fuel pressures; and, in addition to this, the achievement of stable combustion in the low-load operating range.
A comprehensive analysis of injector spray characteristics was conducted, leading to the development of a Honda-made high-efficiency, high-pressure fuel supply system. This enabled the achievement of a 15 kW increase in engine power.
Note: these F1 injectors flowed 100 L/hr, so that's 163-ish lbs/hr of gasoline. Droplet size 17 um leaving the injector. You would need a carburetor booster, with 24 holes, and 1450psi in the float bowls to even start thinking about coming close to these numbers, and that doesn't even get into pulse width, etc.
With the availability of DI high pressure pumps, I'm surprised no one (that I know of) has played with a high pressure port or shower based FI system, despite the well documented improvements.
