It's normal - but not good - if the attys have been used and not cleaned. The only time my 510 attys get very hot is if they are gunked up and need to be either cleaned or replaced. Using the cone isn't the source of your problem.
How long have you owned/used this kit?
Have you ever cleaned the attys?
Attys need to at least be rinsed out several times a week with
very hot water. Beyond that a weekly dry burn needs to be done to remove the caked on gunk on the atty coil.
See here for my reply about another hot atty turning into a dead atty problem and cleaning:
http://www.e-cigarette-forum.com/fo...-i-think-one-my-attys-dead-2.html#post4649362