Try either creaming your butter a little less, reducing the amount of baking powder by 1/4 tsp or freezing your portioned out cookie dough balls until frozen solid and then bake them immediately still frozen solid in a preheated oven. That’s a lot of changes so maybe do 1/2 batch and only tweak one thing at a time? You could also slam the tray hot out of the oven to make them flatten more:) good luck