I’m using a 14’ St. Croix with a double spey cast. I figured out my problem was the way I was lifting my rod into the firing position was wrong and the momentum was carrying my “D” loop around behind me (upstream) so the line on the water would curve around my leg, I don’t know if that makes sense or not. Anyway I changed the way I brought my rod up so the “D” loop now goes strait back, (towards shore) and that has been a big help. I know your right about slowing down and letting the rod do the work but the urge to put more power into it to make it do what I want is so irresistible, I see the same mistake happen so often with beginning single hand casters.
Thanks for your help