Huh? Ampacity shall not be less than 1/10 of OCPD.
So lets see 400/10=40A
Is #10 awg cu less than 40A? Where does it say if wires are in enclosure 1/10 does not apply?
My example assumes 75C terminations.
If you read the 10 ft tap rule in its entirety, you will see that the one tenth part only applies on the condition that the conductors leave the enclosure. It doesn't directly say that it doesn't apply when they don't leave the enclosure, but it is a logical consequence of what the rule does say.