One of the challenges for these boards is to keep a balance between making tall hills but also keeping the boards to a manageable size. But limiting the hills to 3" height leaves the hills a bit less impressive. So I've taken some left over insulation board and built some hill toppers.
Not much to them. I cut two layers of insulation board and an MDF base. Stuck them together with carpet tape, and then did some shaping with the hot wire cutter and utility knife.
I left space for a little step, just wide enough for an infantry figure.