BB,
You say your form may not be the "best." How long have you been shooting?? You may be getting the cart before the horse by trying to tune too much too soon.
Can you shoot fletched arrows to a decent group at 10? 15? 20? yards?? IF you can shoot paper plate sized groups (or smaller) at those distances, then tuning might be for you. If you are still working on good groups then just shoot your (really stiff) 2018s and work on good groups. They will group and group tightly IF you are consistent with your shot execution.
Brian, It should really start with grouping and not tuning. Almost ANY arrow spine will group if you do your job but if you are at all inconsistent, tuning will be frustrating, aggravating and disappointing.
Arne