OK, I've thought about this, and right or wrong, here it goes...
Nicotine may be higher in burleys and may be even higher in aromatics if we sent it out to be tested. But, because of the acidity in Virginias, we get a bigger punch of nicotine from the smaller amounts of nic in "some" dark Virginias. PH affects how the nicotine is delivered to your system. Whereas, some heavily topped burleys which may have an underlying oasis of nicotine, just doesn't deliver the punch, because the PH of the sweet toppings makes the delivery slower. Thus, an aromatic could have "volumes" of Nicotine, with most of it just hitting the bulletproof vest of our tongue. Whereas, some darker Virginias that are not especially high in nicotine deliver a more pronounced headspin, because of the armor piercing qualities that the acidity gives the nic.
What do you think?