Ok that helps. Sounds like you have effectively been vaping at to high a wattage to start with. I started at 7-9 watts, then 12.5 - 15 and now find myself bouncing around between 12.5 - 25 depending on the juice since as you have realized they have different sweet spots
You can use the
Ohm's Law calculator to see the effective wattage of a coil based on battery voltage. Plug in:
1.95 Ohm coil
4.2 volts for the battery
And you you will see you are hitting about 9 watts off of a battery fresh from the charge assuming very little voltage drop from your mod and atomizer.
Now, decrease the volts to say 3.7 for a depleated battery and you'll see the watts drop down to around 7.
Now go through a couple of batteries and pay attention to what you like best, the fresh battery? depleated battery? midway? and you'll know what wattage you currently like and can start to target your builds based on the ohms required to get the wattage you like.
After a short while you will learn to recognize when your battery is getting low by the change in the vapor and flavor.
Odds are that over time you will also find that you want to start increasing the watts thus lowering the ohms of your builds.