What method are you using?
Direct percussion with copper bopper reduction, I like to use a large size bopper. The greater mass of a larger bopper just seems to drive bigger flakes for me.
The strength of your platform is critical. Thin edges just can't support big flake removals. They crush and give up a smaller flakes because they are too weak.
Initiations from thin platforms create thin flakes that are prone to step because they are thin and easier to break.
Thicker platforms with initiations closer to center line create thicker flakes that are stronger and less likely to break off.
Yellow wristing (hitting too softly) delivers enough energy to initiate a flake, but doesn't deliver enough energy to keep that flake traveling till it runs out of the rock some where.
If you are doing ABO, none of this applies.