Right now, I'm not mixing anything, but I'm guessing in the palm of one's hand or about an inch inward, on the fingertips. Just make sure your fingers are pressed together tightly enough so nothing seeps through.
I'm not saying this specifically about the products you're using, but I have read that some ingredients/products shouldn't be mixed so we all need to be smart about investigating if the items we want to mix are compatible. If they aren't, and we're mixing them, we could end up with ineffective or even bad results.