At least one is recommended for each individual Grow Area. (Clone, Veg, Flower, Processing) etc. They should be positioned in the Center of the Room , under the lights, suspended so that the BOTTOM of the Smart Sensor, is right at the top or just below the Canopy level to get accurate measurements at the leaf level if Growers plan to utilize the more accurate VPD measurement to assess plant transpiration.
Adding more sensors in greater density , allows measuring smaller and smaller microclimates within a single room 3 , 4 , 5 , 6 – Sensors could be added and if so distributed equidistant from one another to provide uniform coverage areas.
Also additional ones could be positioned ad-hoc in any places that are of interest to the Grower , perhaps anticipated problem areas – Light ingress, Cold or Hot Spots, poor Air circulation etc…..