I provided some screenshots for you to follow along with. There are four images, and each corresponds with one of the following paragraphs: (link is only visible to registered users)

When setting the low pass filter of the Curve to it's highest slope, which is 48dB/oct, you will notice that the filter brings down your target cutoff frequency by roughtly 10 dB when the Q is set to 0.71 (the default). In this example, my target frequency is 60 Hz. (view image one)

We can fix this by setting the Q to 1.0, which doesn't add or subtract volume to our target frequency. However, we end up with a 6 dB boost in the higher frequencies above it, which may not be desirable. (view image two)

To counteract this, we can use a notch filter to cancel out this peak. First, we target the peak's center frequency. I discovered that a good approximation of this is our original frequency times 1.5. It's important to use a ratio for this because Curve's graph uses logaritmic frequencies. In our case, our peak center frequency is 60 Hz * 1.5 = 90 Hz. (view image three)

Once we have found our peak frequency, we can use our enabled notch filter to bring it down -6dB, while leaving the Q setting as 1.0. This will give us a fairly flat EQ curve with a sharp cutoff slope that begins at out desired frequency (or very close to it). (view image four)

Note: I could have chosen a more accurate ratio for the peak frequency, but I felt that the simple ratio of 1.5 is easy to remember and is an acceptable approximation for the peak frequency. It also works well with the default Q for the notch filters.

Hope this helps!