Section 4.3.4, item 48 of the [yellow paper](https://github.com/ethereum/yellowpaper) states the has nonce, n, must be lte 2^256/`current difficulty`. The effect of this, assuming `current difficulty` is < 2^256, the range of the nonce gets smaller, making it easier to validate a block due to less possible nonce values to try. This seems counterintuitive to the purpose of increasing the `current difficulty`. Am I missing something?