If you are using a foam base, another easy was to create a grade is to cut the foam you want to incline, use some 3" nails to hold it in place then spray a low expansion foam (Great Stuff for windows and doors) underneath the riser. You will have some time to adjust one the foam is spayed. Remove the nails once dry. This creates very smooth transitions and has worked well for me in the past. And foam that leaks out can be cut away or turned into scenery.
