it is really straight, i printed a black rectangle in the middle of an a4 paper and cutted it with an exacto knife, it must be straight. I just used normal thin copy paper to test. The 22cm x 9cm are pretty close to the top and bottom and he handle as well. Print equipment recommends a much smaller rectangle. I havent thoufht about the taper thing at all. I thought that only matters with tapered mugs. Is the mug really that bad? They are duraglaze 11 oz mugs with black logo on the bottom