Well this is exactly How I work it. Moving on level open ground has the following starting difficulty:
Walk Mundane
Run Mundane
Fast Run Routine
Spring Easy
Dash Light
Terrain condition increases difficulty by one level for each increase of level, which are Light, Moderate and Heavy.
Possible terrain condition are wooded, underbrush, roughness, slope, and slipperiness.
Conditions are cumulative, so walking through on ground that is lightly wooded, with moderate underbrush would bring difficulty up by 3 levels. So walking in combat through that terrain would be a Light Maneuver.
I use the percentage column of the maneuver table to determine the distance traveled. A fail result in the character tripping over something. I determined how far they got before tripping by removing difficulty levels until I get a percentage result. They fall prone at that distance.
A fumble is rolled on the fumble result.