Not author here. Just trying to help.
In my opinion what the rules say is that you add all dice values combined (in your case 4) and you compare it with your wounds (in your case 3).
If the dice total value is less that or equal of the wounds number you die.
(HD)d6 =< num wounds _then_ die
So more HD less chances to die, because more dice. More Wounds more chances to die.