Wish: Avoid false Right Clicks by narrowing the Right Click area

After being away for a while, I'm returning to BetterTouchTool with the hope it can help me with false Right Clicks on my Magic Mouse.

The problem is my right index finger often strays past the middle of the mouse, and many of my intended Left Clicks become Right Clicks. Since I use my right middle finger (which hovers near the right edge) for a Right Click, having a narrower Right Click area should not be a problem.

I've experimented with Single Finger Click Middle range setting, but I can't move it past the middle of the slider bar. So any click to the right of the Middle point becomes a Right Click.

Are there any other options with BTT 3.560?