You might want to try making various sorts of terrain harder or easier to move through for extra variation. This is easily done: simply roll one, two or three D6 for a unit moving through the terrain. You must decide first on how tough you think the terrain should be. The more dice you roll the easier the terrain is to move through – so you might decide a muddy field is three D6 while a tidal mud flat is one D6. This can also be used to represent moving on worlds with particularly high or low gravity in comparison to Earth – for example on a high gravity world you might decide that you roll three D6 and pick the highest for movement even when you are crossing open ground.
Varying Terrain Difficulty
Source: Core Rulebook 3E, p. 44
An optional rule for rolling one, two, or three D6 (picking the highest) to make specific terrain, or high/low gravity worlds, harder or easier to cross.