When you use intersect underlying, the values of "Intersection shift" and "Min intersection shift" are very important. They control the result. Think of these as a range of altitudes. Coverage only modifies where the intersect sits within the range defined by "Intersection shift" (at coverage 1) and "Min intersection shift" (at coverage 0). If coverage is not having much effect, you need to give the "Min intersection shift" a much lower value (more negative). The larger the difference between these two values, the more flexible the effect it, and the more it allows coverage to affect the result.
This feature is difficult to explain and provide support for, but if you get a feel for how it works it can be useful sometimes.
