I think your max price is a little low. In California PG&E territory the top tier costs $0.40 per. If you have the EV plan it can cost up to $0.44 during daylight hours in the summer.
I think using what is basically a penalty rate that an electric vehicle owner agrees to in order to get cheap overnight rates as the max would also be a mistake. Those customers pay ~$0.12 to charge overnight.