Spraying the underside (side facing the soil) of the leaves would be better, Stomata are located there. Also, there are a low percentage of Stomato are on top of the leaves as well. So, spray both side.
One thing I would recommend you, is not to spray at night. 1) Due to lower night temps water molecules will not evaporate fast vs. during the day. When the water stays on the leaves for more than two hours when the temps are between 60-75 degrees, that will causes lots of fungal diseases. It would be better to spay them early morning before sunrise or early afternoon like 5-6pm. That way leaves will dry before the night or before it gets hot during the day. 2) Most plants (except a few that grow in desert), have their Stomata open during the day for gas exchange and closed during the nights (however they do keep a very low percentage of their Stomata open during the night). So we come back to number one issue- water will just stay there for the rest of the night, best environment for fungal disease to colonies.
If they are kept in shade during the day, you can mist them couple of times, but they have to be in shade meaning no direct sun that hit the leaves.
Spraying fungicide or insecticides at night would be just fine.
Good luck,
Navid.