Making many smashburgers - later ones have inferior crust

I have a question about making many smash burgers. I've been making smashburgers on a Lodge cast iron griddle on which I can fit about #6 2oz patties in one go, which makes 3 double burgers. However, I've been in some situations where I've had to make ~10+ burgers on the same griddle, in which the burgers after the first round tend to have an inferior crust. This is despite me preheating the griddle between batches to ensure the heat stays up. I feel like after the first couple burgers, the cast iron becomes seasoned with the grease and more nonstick, meaning the patties don't stick as well onto the griddle and the crust isn't as deeply caramelized. Has anyone else had this problem? Any possible solutions?