My case binding corners went from hot garbage to clean in about 3 weeks

I finally sat down and compared my first journal from last spring to the one I finished on Sunday and the gap is honestly embarrassing. Back then my corners puckered on almost every book, like 8 out of 10, and I kept blaming the glue. Turns out I was cutting the turn-ins way too short and not mitering at all, just folding the cloth over and hoping. I switched to leaving about 3/8 inch past the board edge and trimming the corner at a 45, and the last batch of 12 came out flat with no bulges. Same paste, same cloth, same press, so it was all in how I prepped the corners. Now I'm wondering what else I'm doing the hard way, so what was the one little prep step that changed your covers?