What I found is that it's pretty easy to be inconsistent with cutting - I had to be sure to have the cut for the top of the triangle, end at the top seam line - not the top edge of the fabric.
I am using a 45 degree triangle ruler, flipping it top and bottom to make the cuts, so I took a little extra time to be sure I was making the same cuts each time.
I think the next time, I'll mark the ruler with painter's masking tape, so I get the same cut each time!
Hope this helps!
Linda