In the Director's Cut article in Firepower 1, Jervis mentions that the playtesting team had to ultimately leave out a special rule for infantry seeking cover behind tanks while advancing. While the rule was interesting, he claims that they were never able to find a simple wording that would preclude abuse and exploitation by rules lawyers. I was giving the rule some more thought and realized that you could articulate it clearly if you paired it down a bit. Below is my simplified version of the rule... what do you think?
Advancing Behind Vehicles
Infantry units may use vehicles in their detachment for cover when advancing towards the enemy line. To do this, arrange up to two infantry units (not cavalry!) behind each vehicle and in base to base contact. The vehicle must not be a skimmer, walker or something small like a bike, and must be from the same detachment as the infantry. The exact arrangement is flexible, but should be visibly appealing and logical. As long as they remain in base contact, these infantry units count as being in cover against incoming attacks. This cover is lost if the attacking detachment has any unit that both has line of sight to the infantry and is positioned behind an imaginary line drawn between the infantry and the vehicle (that is, behind the vehicle). Alternately, infantry units can be placed on either side of the vehicle (although all infantry must be placed on the same side) to protect against flank attacks. Draw a line along the side of the vehicle between the infantry units and the vehicle to determine cover as above.