I was speaking strictly in terms of fuel drop out issues in some manifold designs using a wet nitrous system, but you did bring up a point.
In terms of DRY type systems with a single nitrous injector (or nozzle), changing even the smallest aspect of the engine airflow can disturb the nitrous distribution. This leads to some cylinders running either too rich and others too lean because of the fixed aspects of using fuel injectors for the supplemental fuel.
For others stumbling upon this post, this is why the use of wet systems is what we mainly go for. By avoiding the issues and complexities of using a dry system, we can get great results with ease. And even if more of the wet system (single point injection) mix reaches a cylinder than others, at least the A/F ratio will not change and there is less danger to the engine. With WoN, the danger is very minimal as smaller nitrous doses can improve engine reliability as opposed to generic systems that greatly reduce it.
The risk in a single point wet system comes at the point the manifold increases the chance it takes for fuel to fall out of the mix and this can happen for a number of reasons. Mainly, A) the time it takes for fuel to get to the valves, B) centrifugal force acting on the fuel from harsh bends in manifold airflow, and C) gravity acting upon the fuel when airflow travels upwards. Of course, there are more aspect to this but those are the main issues and they can exist in combination.
Avoiding such issues on single point wet systems can be done simply by adding a progressive controller (up to a point), and/or converting to direct port. Progressive control helps the intake manifold deal with amount of nitrous/fuel mix so that fuel will have less of a tendency to drop out, but there is a point where progressive control will not be enough. By converting to direct port, the N/F mix bypasses the function of the intake manifold so that the mix remains even and arrives at the valves easily. The result is increased reliability and more greater power increases.
Now, the one caveat is when the engine/vehicle design doesn't lend itself well to installing a basic direct port system. At that point, more extensive and radical changes to the vehicle may be required in order to accommodate installing the DP components correctly, which is vital for correct nitrous/fuel distribution before it even reaches the induction system.
