Something else to bear in mind is that taking a steady dose of nicotine keeps tolerance high. Having spikes and lows allows the tolerance to reduce and lower amounts of nicotine to have greater effect.
I vape zero or low/6mg constantly until I get a craving and then I have a couple of drops of medium/11mg or high/18mg for a spike. That is much more like smoking and gives me far better effect than a constant dose.
Over a day I maybe vape 0.5ml of high and as much low as I want. I'm trying not to use more than 24mg per day and spikes are a great way to stay within my allowance but still get good effect.