Since we all know Don (DRG) likes nothing more then players telling him how to do his job...
In the game fortifications (unit class 0) are treated basically as immobile armor units. This works pretty well vs every weapon type except ATGMs (weapon classes 13, 20, 21, 22, 24, and 24). Until the advent of the Sagger and TOW in the 70's fortifications make an attacker work for it.
The problem is ATGMs use HEAT warheads, which work by burning a hole usually less then 1 cm around thru the metal armor of a tank and spraying the interior, ammo, and crew with molten metal. It's rather difficult to melt thru a dirt or concrete fortification and I suspect hot dirt or concrete dust is somewhat less effective then melted armor.
Increasing the HEAT armor rating of fortifications would have the side effect of making them too resistant/immune to RPG/bazooka type weapons, the exact weapon types (in addition to flamethrowers and satchel charges) traditionally used to assault them.
Altering the game code to prohibit ATGMs from firing on fortifications has the side effect of players screaming that the game won't let them fire their weapons.
Maybe adding code to double, triple, ten-fold (whatever's needed) the HEAT armor rating of fortifications vs ATGM weapon classes will work.
Two questions for the peanut gallery.
1) Is ATGM vs Fortifications a big enough problem to require a solution?
2) Do you have a practical alternative suggestion on how to solve the problem?
** Watches Don turn purple then runs for cover **