If you are making a picnic blanket I am wondering why you need the 8.5" block. It appears to me that you would be easier to alter the large block cut from the fat quarter rather than all those very odd size smaller squares for your 9 patch. For me it would be too much aggrivation to deal with an odd size smaller square and more precision to get it exact. More flexibility in the larger squares and considering all fat quarter are not the same size.