Try switching one to a different attachment position and see if there is a difference. If that doesn't work, you might have to get out your saw and make the wood part of the stabies smaller.
I had problems with this last year. I had the stabies 2 sizes smaller than the biggest (the wood ones from murray's) and they didn't do enough to counteract the rolling. So I moved to one size bigger. Well that size actually had the same size lead on it as the smaller size and the only difference was a bigger piece of wood. This resulted in the stabies taking longer to sink than the roll of the boat and I actually busted one of the pole mounts when I was running with only one stabie in the water. I'm putting on new mast and poles and will try the largest stabies. If I have to cut them down a bit to get them balanced right I will do that.