It took me awhile to understand the quilting also.
You have your block and you would start quilting at the top of the block in the middle by the seam and go to the middle of the next side of the block and then to the middle of the bottom of the block and up to the center of the middle block and end at the top again. So that you would have a diamond type shape. The longer blocks would have a longer diamond in it. You could mark it or just kinda eyeball the line.
You know how all the different sizes make of one big block- But you would not be stitching the whole big block but the invd fabric blocks that make the larger block.
I hope I did not confuse you, because I think I am confused now.
I hope to try it this weekend and I will post a picture of it.