I have been messing around a bit with the Eddie Bravo twister "banana split" and calf slicer, and the majority of the time I attempt the calf slicer, I come across the same problem . I have everything locked in correctly, but when I pull down on their leg down, it actually hurts me more than it hurts my opponent. The reason for this is that since my legs are figure-foured, I am actually applying the calf slicer on myself.
I asked this same question to Kristian Woodmansee at one of his clinics. His answer was to "pretend that their leg is like the lever on a nut cracker". I have tried this, but it doesn't solve my problem. I have seen other people have this same problem, so I assume that there is an easy solution.