Sewing hundreds of HST blocks is always followed by pressing hundreds of HST blocks. In the past year or so I've migrated more toward pressing my quilt seams open, especially on HST blocks. Since I don't know exactly how these blocks are going together I want to avoid too much bulk in a seam. I'm solving that by pressing the seams open.
One day when I was pressing seams I noticed a long-forgotten tool that I used to use in garment sewing called a seam stick.
A seam stick is a half round piece of hardwood. You align the seam along the curve and then press the seam open. The hard wood surface opened that seam and helps to press it as flat as possible. The curved edge keeps the iron touching only at the seam so there's no impression of the seam allowance on the right side of the fabric.
You can really tell the difference in the flatness of the seam when it's pressed with a sean stick.
You could make one of these yourself if you have some basic woodworking supplies and a large dowel. I also found 2 versions for sale. One is the original Seam Stick (like I have) and the other is the Strip Stick. I do find that the steam from the iron will eventually raise the grain a bit but a quick sanding with a fine grit sandpaper renews it perfectly.
If you haven't been happy with your pressed seams this might just be the additional tool that you need.