What are you trying to grow? Why the need for a full 16" of straw? If you dont shread it you won't be able to pack it as densely and that may help. Another thing that I have tried that worked is after shreading/pasturizing, place 4" of straw, spawn, 4" more of straw and then one of those "egg crate" Light difuser panels for ceiling lights, with more spawn, 4"straw,spawn, 4"more straw and more spawn with a light sprinkling of straw, then use another panel and some weight for compression. You could even use the panels every 4" and since they are plastic, they are reusable.------------------
-ChesterCopperpott-
"Old enough to know better, Young enough to do it anyway."