Then don’t rely on the markings on the bottle; measure it out with an insulin syringe, as those are usually accurate. You can buy them at a pharmacy; they aren’t expensive. You need to put 6.6 or 6.66ml into each of the 6 bottles from the total 40ml of nic shot. If you’re lucky, there’s actually 10ml in each of them. But I’ve had it happen before that there was only 9ml in them. Although that didn’t happen recently… If there were only 9ml in them, then 6ml is the solution.
As for the mod offered by Zoli, I think you should accept it too. Especially since your mods are smoking! You know the saying: If they offer, take it; if they hit you, run away!