I can't speak to the 40 Comp. All mine are 35's. I've found that during range finding it helps to focus my eye on reticle detail ( such as a MIldot) until I get close. That help preventing with my eye changing focus due to the clarity of the Leupy image.
I range far to near, pass through the focus so I know what clear is, then return and focus the wheel until the image just begins to blurr on the far side of the focused image null band.
Very accurate and repeatable, however you have to note that due to the span between markings on the Comp series scopes it's unlikely that you'll come back to the exact same spot. What I look to accomplish is to learn the scope until a rangefinding sample of 10 tries end up in a band of 1 1/2 yards width from 50 to 55 yards.
I've had to calibrate all my scope for temperature. Once done they're freaking repeatable.