Let's discuss the design of the equipment seperately
There is an empirical dependence on several features of equipment design. Let's list some of them:
a) The side of the holes of the grid
b) The features of nozzle that moves the solution to the grid (the maximum amount of liquid per minute, spray spot)
c) Air pressure on the grid
d) The volume of air passing the grid per unit of time
The ideal ratio of all these factors for the particular device makes it possible to achieve the maximum volume of foam. But the following factors may prevent you from reaching it.
1. A very small holes of the grid prevents optimal solution or air movement. The foam will come out slowly. It wille be watery. You will have less foam.
2. A very similar reason is when there is a little air supply, and the solution supply is large. Even if the grid has not very small holes, the foam will be watery and will have smaller effectiveness.
3. A very big and strong air flow can prevent the foam from foaming in full scale. The flow might be so strong that the parts of the solution will fly out in the form of the initial liquid, without forming foam.
4. A very big and strong air flow can burst foam at the outlet, after its formation. The foam will fly like snow. It's beautiful, but the final volume of foam on the flow will be less.