I do not know the answer, but someone will, I am sure. In the Stack and Whack patterns, it is not something I really pay attention too, just following directions from Bethany Reynolds books on the subject. When its cut on the bias, the bias can stretch or be pressed so its out of alignment with a block. That I have experienced. If the pattern shows the grain lines two different ways, it probably is important to pay attention to it in that pattern and mark it on the piece cut out.