If one side of a fight can't attack at the current range then, as you guessed, no harm is done. For both your cases, the most important thing is what is happening in the game, what makes sense in that context. Think about what would be the case with real monsters and hunters in that situation, and apply it using your moves.
If a hunter is, for example, sniping at a zombie then it probably won't be a kick some ass move at all. In that sort of situation, I'd just use my Keeper move apply harm as established. Kick some ass is intended for when the hunter is exchanging attacks with their enemy, so if one side isn't doing that it is usually not called for.
Closing on an enemy with greater range than the hunter would usually be an act under pressure (where the pressure is keeping out of the way of attacks). The hunter may wish to read a bad situation first, hoping to get +1 ongoing to use as they get in to range. Another way is to have someone protect them and use the "all danger is focused on me" option. Or use magic. Or they could do it totally in the game fiction, based on the terrain the fight is happening on. E.g. "while it spits flame down the alleyway, I duck into a building and start working my way through it until I can come out behind the monster."
Does that all make sense? It's early in the morning here and I feel the answer may have got overly wordy.