Actually, it doesn't matter how the edges of the fabric are lined up. All that matters is whether your ruler is a perfect 90 degrees from the fold. Any deviation from 90 degrees will result in a "V" at the fold.
Once I line up my cutting ruler, I check its trueness to the fold by butting up another ruler to it. If the first ruler is true, the second ruler should line up perfectly with the fold for its entire length. If it doesn't, I adjust both rulers until my cutting ruler is perfect.
If you think about it, you realize that you can also cut bias strips this way. How the ends of the fabric line up don't really matter in terms of getting a straight strip without the "V" at the fold. Grainline is a separate issue from the dreaded "V" at the fold.