I don't think that your imbalanced load, while not the most desirable condition, is going to affect your demand metering. The way that demand charges are applied, as I understand it, is that your highest monthly demand over a prescribed period, whether that be minutes or hours, is used to compute your demand rate for the next xx amount of months. It depends on the tariffs in place in your area. The utility assumes that they are going to have to supply that load at any given time for any given amount of time, hence the charge.
Our utility colleagues on the forum will no doubt chime in to help on this one (I hope). Charlie Eldridge ?