Hot take: taper lever halfway up is not a magic fix, and I can prove it from my chair
I keep hearing guys say just flip the taper lever halfway when a fade looks off, but last Tuesday a kid in my chair at the shop on 9th ended up with a line at his temple because I did that instead of adjusting my blade angle. The lever only changes the blade position, and if your wrist is flat against the head it still cuts the same length no matter where that lever sits. So which is it, do you set the lever first and then move your hand, or do you fix your angle and leave the lever alone?
Setting the lever halfway only does something if your blade angle lets it matter. I've tested this on myself and on a few heads at the shop, and if you keep the blade flat to the skin the lever is basically just decoration. The teeth are still the teeth and the gap is still the gap.
Where the lever actually earns its keep is when you tilt the blade so you're cutting with the tips instead of flat. Then moving the lever back opens up the gap a bit and softens the line. But if your wrist is flat and you're dragging the clipper up the temple, halfway does nothing but make you feel like you did something.
That line on the kid wasn't the lever's fault, it was the angle. Fix the angle first, then use the lever to fine tune.