2 Temp Humidity sensor Pro units give different readings

I just received my second DHT Pro sensor and added it to my project. In my test environment, both sensors sit right next to one another. After 24 hours of running, the temp readings from both are identical or very close (same or within 1 degree F). Humidity readings are 10% to 11% different. My program tracks min and max readings, and the same pattern shows up in min and max, as well as in the current readings.

I am using these sensors on a GrovePi, and the same library code is being used for reading both units. My code just makes 2 sequential calls. I recently bought an Arduino and Grove shield - will test on that once I get up and running. But my project needs to run on a RasPi. So I need help figuring out why these readings are not very close.

Note: the reason the sensors ended up next to one another is that using longer wires produced huge number of IO errors. I am addressing wire length in a separate post. Mentioning it here bc the purpose of my project is not to have two DHT in the same place; but to manage environment in a building with one of those sensors inside and other outside. Having discovered this large discrepancy, though, I need to solve the problem before I can trust readings in the indoor / outdoor configuration.