I am just learning this stuff. This is my line of thoughts on the subject.

   The amount of fuel that will flow through the injector during a
pulse width, is proportional to the pressure differential across the
injector.
(Delta Pressure) * (Pulse Time)  =  constant * Volume
  Without the "Vacuum Regulator", at Idle when you have a vacuum
(less pressure) the Delta Pressure would be bigger, flowing more fuel
per pulse time.
  I guess the computer wants a constant flow rate. The manifold
pressure could change significantly during the intake cycle. Cycle
time inversely proportional to rpm. The pulse width is proportional to
rpm. So, as we need more fuel we have less time to inject it. And
during the injection time, whithout the vacuum regulator, the flow
rate would change, being less predictable for the computer.
  I think you would want the injector open over most of the intake
cycle to get the best mix. Maybe starting a little late so as not to
be flowing fuel during the exhaust overlap. I'll pick 79% for the duty
cycle of the injector. Since the rotary's manifold is always in the
intake cycle we would want the injector open 79% of the time. Which is
also 79% of the intake cycle.
In one rotor rotation:
close    open    close    open    close    open
7%    26.33%   7%     26.33%   7%    26.33%
But in one shaft rotation it is:
close open
21%   79%
  Is this what you want at full power WOT?
  Now I understand the desire for staged injectors. At lower rpms you
can keep the lower flow injector open longer  getting a better mix.

--
Blake C. Lewis