The additional statement for Line 20 on K-1 is typically on a second page of the form and is not obvious and quite easy to overlook. It is often in a small table format, and you should see the Z and then an explanation 199A and a number. If you don't see the Z look for the 199A.
Often, it is buried on the same page that all of the explanations/instructions for the boxes are on, and so it looks like it is just part of that same small type. You don't want to enter zero, as this is an important deduction for you - it will likely help lower your taxes!