I did a very tight grid in design of say 10 feet and it completely changed the flow pattern to exit a boundary. How is that possible and then if your design and export are not the same will you get something different for control than what was seen during design?
Grid design spacing will be the basis of OptiSurface to calculate the proposed surface using the indicated parameters. Once the surface is calculated, then this will now be the basis of the export.
Changing the grid spacing for landform design will likely change the proposed topography. The calculation engine can only optimize with the data it is given. The data it is given can be quite different on a 10ft grid vs 50ft grid. Some areas will be missed if a large grid spacing is used, so we recommend to use a smaller grid spacing, say 20ft, for your final calculation.
Changing the export grid spacing will not change how the surface will be as it is based on the proposed topography. It is not advised to export on a grid larger than the design calculation grid because you could miss flow paths. This is particularly important for 4Way designs. Best practice is to match the calculation grid spacing and the export grid spacing.