HST and QST are frustrating to get right. I believe the quilter has to work out a system that works best. I made two quilts that half are one type and half the other. I make the initial squares larger and cut down to size. This is the case when I got the correct size square ruler. Sometime I press the seams open and at other times to the side depending on how the piecing is done. To get quarter squares to match up in the center and on lines. I pin the centers down into a cork hot pad. This holds the centers while I line up the longer seams. This works for me and students are amazed how well they fit.