bgoracy,
On the one hand, the response you got from ProVape makes some sense. Again, if the carto resistance drops
transiently to below 2.48 Ohm, that will trigger the wattage protection.
I don't know, but I think ProVari's circuit "feels" sudden changes in resistance as well somehow and throws E1 to "preempt" a hard short. I had a few cartos have a partial short (basically a part of the coil shorts). In this case the resistance dropped suddenly from 3.0 Ohm to 2.4 Ohm. The ProVari threw E1 right away, but then, after I checked the resistance, it kept going because the new resistance really was okay for the voltage. Sure, I tossed the carto, but you get my point, I hope.
On the other hand, I don't think this should happen
every single time, like you describe.
Third, you may want to try a good quality 3.0 Ohm atomizer. I really don't want to burn my carto trying 6 volts again, but I have been firing my 3 Ohm HH .357 at 6 Volts (blowing on it without vaping, it's too much for me) for the last half hour without E1. It's now really hot, so I'll stop - I already took an expensive risk

Cartos tend to have flimsy coils that maybe are more unstable at 6 V. I really am speculating, though.
Lastly, I really think that if this thread is not moved to the
ProVape then you should probably post there as well - the suppliers are not allowed to reply in here, they can only do so on that forum.