The sha1 hash for 64test64xa is 6779c53432b8badf049bb9d8924a5785dd887243 which is 41 characters only using hexadecimal, 10digits and 6letters. But how long it would be if it was using the whole 26 letters in the latin alphabet? What if it also differentiated between UPPER and lower cases?
Yeah you can always take a hex hash output and convert it to Base64…which does conpress it significantly. Apply LZ Compression and boom.
You didn’t convert a hex number into Base64, you Base64 encoded the hex string.
TL;DR, you used the wrong tool.