Drats, you're right. I thought it'd be worse, but the ratio seems to only depend on the number of letters in your character set: 1/count(letters in alphabet).

For ascii at 95 printable chars you get 0.9894736842. Makes intuitive sense as the "weight" of each digit increases, taking away a digit matters less to the total combos.

Maybe I'll start using one Japanese Kanji to confuse would be hackers! They could spend hours trying to brute force it while wondering why they can't crack my one letter password they saw in my terminal prompt. ;)