Good point. I always assume the shot itself and nothing about the player's personal quirks, when I'm talking about margins.
Maybe it needs to be honed. I see people struggling against slice backhands more than topspin backhands, yet the latter is the more widely used. More often than not, shots like these are good for, at least, setting up a winner off the volley.
But I'm going to come to the net much more tomorrow, using this style and seeing how effective it is at winning me points. With slicing, I just find that there's a lot more to judge, to balance placement and power. Even though it's "supposed" to allow more room for error, it really just widens the angle and decreases the margins, like you say.