The idea of high ohm high voltage vaping is not going to be what you are thinking it will be. The sig has limits, and ohm's law cannot be beat by a mod.
sig150 limits.
volts 1-7
ohms .15-3
watts 10-150
at 3ohms and 10 watts, you are already at 5.48volts, you reach the 7 volt limit at 16watts
at 2ohms and 10 watts, you are already at 4.47volts, and reach the 7 volt limit at 21watts
at 3ohms and 100 watts, you would need 17.32volts
Just happened to notice your Calc are off
At 7 volts into a 2 Ohm load, you're at 24.5 Watts.
Your 3 Ohm should be 16.33 Watts but that could be rounding.