There are a few reasons why no two plants require the same amount of CO2. I'm not sure why people expect that all plants must behave the same way and have exactly the same characteristics and requirements. Each species has strengths and weaknesses. Plants produce an enzyme called Rubisco. The job of Rubisco is to attract, hold and transport CO2 molecules in order to convert the CO2 into sugar.
There is one fundamental "flaw" in the characteristic of Rubisco, however, and that is Rubisco has a difficult time distinguishing CO2 from O2.
For every 4 molecules Rubisco collects, only 3 are CO2. So when Rubisco dumps it's cargo into the reaction center only those 3 CO2 molecules are used. The Oxygen molecule does nothing, so the sugar production operates at 75% efficiency at best case. These Oxygen molecules causes a LOT of downstream problems because the plants has to waste more energy finding a way to incorporate them.
This wasteful recycling of Oxygen in the reaction center that specifically requires CO2 is referred to as "Photorespiration".
Photorespiration is especially wasteful because the net result of the process is the release of CO2, so it undoes the job of Rubisco.
The reaction center in which CO2 is converted to sugar is called The Calvin Cycle.
So now, there are two ways in which precious CO2 is lost by the plant: a) ordinary respiration which occurs when the plant consumes the sugar it produced and, b) inefficiency of sugar production via photorespiration.
There is something called the CO2 compensation point where the uptake of CO2 through the photosynthetic pathways (Rubisco) is exactly matched by the loss of CO2 through respiration and photorespiration. At this point, there is zero growth and if the carbon loss is greater than the carbon uptake, the plant dies.
Each plant has it's own compensation point. It's carbon uptake ability will be limited by various factors, as mentioned, leaf morphology, not just size and geometry, but also cuticle thickness, which is an obstacle to CO2 and Oxygen uptake, Rubisco and chlorophyll concentrations within the leaf as well as other photosynthetic chemical efficiency.
There are so many variables which affect how well a plant can gather and assimilate CO2. One size cannot fit all.
As Edvert points out, the partial pressure of CO2 may need to be increased, so an injection rate increase can be attempted. It's not clear how the spraybar is oriented and it may be that the flow is not reaching the substrate effectively. More data is needed to analyze the cause of CO2 deficiency.
Cheers,