Question on Alternative Assault Resolution

[TJD]

I'd like to ask for help in understanding Alternative Assault Resolution. As I understand it, the rule requires that a unit's hard attack value must be used when attacking hard targets like bunkers and armored vehicles. I can understand the value of this rule in the context of infantry vs. armor. But it seems to make less sense in the case of infantry vs. Bunkers. Case in point:

I'm playing the _ALT version of Troina in Sicily 43. There is a bunker in that city. The city's defensive values are such that artillery fire is of almost no value against units in that bunker = -%50 for city, -%40 for bunker, +10. The only way therefore to disrupt the German defenders is by assaulting them. (Ordinarily, I would never assault undisrupted defenders, especially high-quality Germans, but as artillery is practically useless there seems no other way forward.) But when the Hard Attack values are used per the alternative rule, the American infantry and even Engineers are almost impotent: the have HA of 1 and 3 respectively, when their normal Assault values are 12 or 14. Even when the German units have been surrounded and had their morale lowered by Isolation and Low Ammo, I'm pretty sure assaults against them will get nowhere with these values.

So how does one take a bunker when this rule is in effect? It seems like an incredible handicap. Am I not understanding the math correctly?

Thanks!

Tim