Humidity always helps rooting clones; think of it like germinating a seed, once it dries your fvcked.
Good question as to if you should start at a specific area however I've not ever had problems taking clones from any area as long as they are takin proper care of. And somethingni just learned is you can clone a leaf. You can also clone a leaf put it in a ziplock and store it in the fridge and root it weeks later.(just be sure it doesn't completely freeze out the clone)