I understand your concern, Noodle. Yes, if you use enough EO then it'll stick to the hair and scalp. But you gotta use a lot of it. i'm talking, more than six drops per cup of water. The thing I always think about when using EO and this has never steered me wrong is this-- the concept of homeopathy and water memory. EO's are extremely concentrated. (Do research and figure out how many pounds of flowers, leaves, etc it take to make one ounce of your EO and you'll be AMAZED!!) You don't need a lot. If you're just going for scent then you'd be best to put a few drops with water in a spritz bottle and spray it through your hair like perfume or just do a plain water and EO rinse. But if you're going for the medicinal properties of the EO and a good strong clean scalp and hair then 3-4 drops in your squirt bottle and a cup of baking soda water mix is really all you need.
Unless you have hair down to your ass, I really don't understand people using more than one or two cups of water on their head. Just get a big enough squirt bottle and there ya go. Shoot that stuff into the roots and all over, soak, scrub, rinse. Voila. Katsup bottles work great for larger-than-a-cup water quantities. I just use an old hair dye bottle I got years ago in a box of hair dye. It holds exactly one cup of liquid. Perfect. I have hair down past my shoulders.
Anyway, less is more most of the time when it comes to EO's. Use too much of the stuff and you'll toss your scalp ph to the Pit and then you'll really have issues. Use too much and it's not only wasteful but it's just bad for ya. It freaks your scalp out. EO's can be both drying and oily/moisturizing. A weird thing to think about, but it's totally true.