IDK what STM is... On my mech that, quad parallel 32 gauge 0.4 ohm coil, would be 38watts and a HOT, juice scorching, wick burning, 424 heat flux. If a STM is some regulated mod I quess it would be vapable at 20 watts or less. But i guess thats the point. There is no ONE way to vape nirvana.
Ways to save $$on Juice, either DIY or Vape less per puff. More likely a combination of the two.