Yes, much better to negotiate when volume was high. I used to trade hundreds of contracts IC each month when I negotiated. I trade less volume now as it was making me uncomfortable, but my commission rate did not change.
It was probably easier to negotiate years ago than now. Getting the ticket fee dropped was easy, but they wouldn't budge on the per contract rate. Then later I contacted Sheridan and got a nice rate.
I've had nothing but very good experience at ToS when I complained about trading problems, which happens only rarely.