I always start ANY atomiser/cartomiser off on a very low voltage...

to break them in slowly and because the rated ohmage isn`t always accurate...
so I turn up the voltage slowly until it`s "just right" for that specific atomiser.

2.5ohm protank type coil end up around 3.7-3.8v

3.0ohm cartomiser ends up around 4.0-4.5v <<< see the difference for coils that are "identical"

coils wound slightly differently, or carto wadding packed a little tighter can make a lot of difference between one and the next...

Just .1v too high on a protank coil can make all the difference between OK and burning wick :)