I want to point out that there are several types of hash.

What I described was yellow hash, the alchohol method I beleive is black hash and there's others (I love Wikipedia)

I will say this though:
If you're getting an 8th of Hash out of a Quarter of Weed, there will be some plant matter in there. Plant Matter = Lower Potency

My Method is very passive in that I'm not actively attempting to create Hash, it's more of a byproduct. With Schwag that has some crystals on it, I get about 2g per oz.

YMMV