The settlement in the low spots or high fill areas is probably due to the leaf matter/stubble that was mixed in the soil.

To get the best results for landforming, ideally you should have no organic matter on the field surface. This can be achieved by burning the organic matter if possible or disking the material in and let it decompose. This can be difficult with a crop like corn.

For this reason, we recommend landforming after a crop that produces less biomass like soybean or rice.

We do have a feature in OptiSurface Designer where we can exaggerate the fill and cut areas to account for settlement in the fill areas and expansion in the cut areas after cultivation. Here's a link to that article: How Often Does The Earthworks Need To Be Done?