Back in the glory days when I could afford Tiptree Little Scarlet and lived where it was readily available, I noticed the various differences between it and their regular strawberry. I am convinced that in addition to different berries, they had a different sugar balance and were cooked differently. Still the best store bought jam for me ever.
I had forgotten to mention using the best possible berries you can find! I always use local fresh ones, living up in the PNW like I do. Good berry growing area.