I had similar problems when I first started using temp control.  I also never go above 20W.  I just don't have a need to. 
Ensure that your 
coils are wrapped tightly & that they're perfectly spaced.  Any warp or imperfection in any part of the coil or it's legs, I have found, can impact quality of its performance when using temp wires.  Of course, there could be a problem with a chip, but as I mentioned, varying resistance in the squape is a huge factor.  A coil that's supposed to read 0.12, for example, I can adjust the center pin and have it read 0.11 or 0.18 -both while totally cold, just by screwing in or out the center pin.  If the coil's resistance is read incorrectly by the chip/device, your vape will either be too harsh (chip thinks coil resistance is higher than it actually is), or it will hit temp control way to fast (if the device/chip thinks the coil's resistance is lower than it actually is).