Correction on Misting Comment:

I've been doing some research, and read that although the stomata (pores used for respiration) are indeed on the undersides of the leaves, when you hit them with liquids, they actually close up! (Not buying this? Pluck a piece of a leaf, put it under a microscope, and check it out for yourself.)This is counter most accepted info that foliar sprays should be applied to the undersides of leaves. So for good measure, it seems worthwhile to spray the entire leaf. I wonder if adding CO2 to the environment first might open the stomata enough that they'd stay open during spray, but I don't have CO2 with which to test this.

When misting simply for humidity, I doubt it matters much where you spray... You're just trying to add moisture to the environment.

Also, research indicates that you should aim for a pH of 5.0 for foliar sprays. So add a touch of pH down, unless your potassium is already to high... Then you may wish to add vinegar instead - but not Apple Cider Vinegar, because this is also high in potassium!