I am convinced that one of the reasons ST sales are so low is because the 6/12 match deals are such good value. A number of people considering a ST will surely plump for a 12 match package instead and see how the season pans out.
I personally would love to go and watch Cov Rugby on the weekends I come up for City games. The two clubs should work together and trial the odd weekend where they do that, perhaps offer a discount off the overall price of the two tickets.