How does the defense value work?

[NikolaiB]

Just one more question. In one of the scenarios that I am playing, there are these one tank HQ units. They have attack and assault values and don't seem to act like typical HQs. However, they appear to die very easily, even though they have the same defense values as the normal tank units.

So, my question is, how does the Finishing Off rule apply to them? As they represent one tank (10 men), this made me think the rule does not apply to them. However, they just seem to die so easily that I want to double check.

PS. I also feel like this rule should be mentioned in the attack/assault modifiers section too.

Thank you for the help!