[Treeve]

It's about the rearmost face which can be contacted by a string line, or by a headform sphere mounted on a pole of variable length and pivoted about the H-point with the seats in the 'least favourable' position.

It's not quite as simple as 'the brow needs this, and the face of the dash needs that'. If you cannot reach anything but the brow, you don't need anything on the actual face of the dash... But it's all interpretation.

The interesting point comes down to the suitability of the material for the padding, and there are specific material densities mentioned for the padding, which are way more dense than boogie board foam.

Treeve