Have you tried the 0.7 coil? It might be able to handle slightly higher VG (if the harshness you are getting is from too much PG). The other thing you can do to thin your vape without adding harshness would be to add a bit of distilled water (you can use up to 10% but I'd probably experiment with a few drops in your tank first.)
I had to use max VG in a N2 tank starting out as I am PG sensitive, (although DW helped) and my coil life wasn't the greatest. I did things to make it work (continuing to inhale after I hit the fire button to ensure more constant wicking, etc.) but my coil life wasn't exactly what you'd call stellar.
I also ran with the air flow wide open. My favorite Nautilus coil happens to be the 1.6 but I'd say experiment with the others if you haven't you may have a different experience.
I wish you luck. The Nautilus coils don't have the most longevity of all time, but I am usually able to get more time out of them by reducing gunking factors (no overly sweet, dark, or gunky juices) although I also use them for the most part in non-nautilus tanks, where airflow and etc is a bit different.
I hope you meet with more success. Chain vaping is also something that can kill small, MTL tank coils off quickly unfortunately, as too much heat build up will really kind of push them. Now that I rotate setups, I find overall coil life in ALL my coils is better (and not only because I'm not vaping as much in one coil) so if you do have moments of chain vaping and don't have a backup setup yet, I might get one, so you can rotate them (having another setup in case something happens to yours is also a bonus).
The N2 was my quitting tank, and I still think it's a good tank, (my husband is using mine for dual use at the moment) but (in my humble opinion as always) the metal cage is great when it comes to drops but it can cause the tank to sort of heat up more as it can be a heat sink. (Again, just my opinion, but I did notice it, etc.).
Good luck most of all.
Anna