Yeah, you should fill your tank FULL when you refill, I mean leave room for an airbubble at the top, but the less eliquid in your tank, the more it will heat up as your coil heats up.
I would also recommend poking a few tiny holes in the coil wicking to help with wicking. If your juice is sweet, dark, and high VG, I would expect gunking issues, which can definitely shorten coil life. An RTA would be an option if that is the type of juice you prefer, as you can rewick more frequently. Look for a clear, less sweet juice you can enjoy in that tank, to help your coil life. Also, if you can turn down your wattage, that will likely prolong coil life as well and you could look at a slightly higher PG ratio in your juices as well, to help with coil life.
Any coil can be killed with the right juice. I had a storebought coco that would kill any coil I had in about 2 days. I DIY and like having more control over not having additives such as food coloring, tons of artificial sweetener in my vape, etc.
Best of luck, hope you get it resolved. If all else fails, I would consider a Uwell Crown (the original or version 3) they are well liked for flavor and offer a wide range of resistances but coil life seems to be good, and the coils don't seem to have QC issues or need to be modified much in order to get decent coil life. You may find it easier to just choose another drop-in tank that may work better for you, and keep the prince as a backup tank.
Best of luck!
Anna