Trying to figure out how Assault works

[Xerxes77]

Weapons carried add different values too, anything they carry has an assault value!

I am indeed taking the weapons into account. Here's the breakdown:
The defending squad is comprised of ten men with 10 AK-47s. The men themselves have an assault value of 10 as per the scenario's Infantry Assault Value, while each AK-47 has an Assault Value of 18.

That gives me a total Assault value of 280 (10 x 10 men + 18 x 10 weapons).

Mapped to the Attack High Loss Value (240), that gives me 280/10000 * 240 = 6.72. As far as I can tell this result means that I should see a maximum of 7 casualties, and not too often! Clearly my calculations are not correct, but why?