40 Gallon Breeder Tank Humidity Question

[Macropodus]

40 Gallon Breeder Tank... helped raise the humidity from the 20's to 45%...

Where is the humidity 45%? We have 3 forty gallon breeder tanks, dimensions 36" x 18" x 18" (we assume your tank is of the same dimensions). The humidity on one side is significantly different from the humidity 3' away on the other side. Just as there is a temperature gradient there is a humidity gradient as well.