In theory, the Borum thermoplastic extruder will extrude an even layer on the surface. This means that if the surface is rough and uneven, the line will be too, following the stones and holes up and down. In other words, the material consumption will be predictable according to the adjustments, not according to the type and condition of the surface.
With the screed box/drag box, it´s different.
As the name indicates, the box is dragged with contact to the surface. Those contact points will determine the line width. The material pressure is by gravity only (material level in the box itself).
In other words, the material will fill up all holes and roughness of the road, meaning the material consumption will depend on how “open” or porous the surface is. This is also why it is sometimes difficult to calculate material consumption.