You want to work with the plant's vpd, not the air vpd. The calculator you are looking at just refers to plant vpd as leaf vpd, you can disregard air vpd as the plant's vpd tells you everything you need to know. From the page you linked to, right above the calculator:Much obliged FourthCity, I will be referencing your spreadsheet.
Just for the sake of clarity could you comment on the vpd calc from pulsegrow that I posted.
https://pulsegrow.com/blogs/learn/vpd#calc said:However, since the inside of a plant is water, the plants feel a different VPD than just the normal Air VPD. If you want to figure out what’s going on with the plant, you need to consider the cooling effect of evaporating water as it exits the leaves’ stomata. To calculate this, you need to know the difference between the air temperature at canopy level, and the temperature of the leaves. An IR thermometer is useful for this.