Do you know when you turn the arm/ fist from vertical to horizontal and it adds snap?

Well try turning it faster whilst tensing your arms as minimally as is possible the less tension there the better.

That will add snap/power.

Next try the same but turn the fist so the thumb points down at a 45 degree angle. This will add even more snap/ power and is more likely to cut them.

Dont telegraph by flaring the elbow too much try to "drill or cork screw" the arm so to speak.