240.(B) is not being used in this application, we are using 240.6(G)
When you read 240.6(G) you find it says 'shall be permitted'
Take that along with the sections in 440 and you get to go much larger that the next standard size.
Here is the reason this is permitted and it is safe.
The HVAC unit contains internal overload protection, if say a motor seizes up the units own over current protection will open before the conductors area damaged assuming you followed the name plate data.
The break at the panel is not being used for over current protection, it's only function is short circuit and ground fault protection.
