I can't say for sure without seeing the operation, but in general... cut area adds a whole other level of containment - trimming, extending, projecting. So for sure the generation should be simpler without cut area.
Seems its worse when the fillets are perpendicular to a vertical wall.
When tilted 5-10* off the generation is very smooth with cut area.
I was not aware until yesterday that it would work without cut area.
Remember you can also change your projection vector. When the surface is perpendicular like youi're saying it is usually better to use an alternate projection vector such as towards drive, or towards line.
A short clarification about the cut area approach:
The basic pattern is created on a drive geometry (explicit or implicit). if part geometry is selected the pattern is being porjected to it along the projection direction. if cut area is defined as well, the surfaces of the part within the cut area are used as before, while rest of the part surfaces are considered check geometry. due to various deasons a continous pass on the drive may be projected such that it partialy touches the cut area and partially other part surfaces that are considered as check. the portion touching the check is trimmed and open ends are reconnected by NCMs.
In a 3X operation, projection along tool axis or along ZM diretctinon near a vertical wall is a common issue that may explain the bad results shown in the picture above. as sugested by others, a different type of projection may resolve the issue. this is only a guess, since it is hard to get to the buttom of it from one picture.
Hope this helps,
NX CAM Product Manager