Yeah I know what you are talking about. I know the engine myself too and, whats's more, I'm convinced If you made them as big as they should be, you would end up finding severe hitbox problems, because as you have said, KF engine allows little enemies only, even when head on (not imposing enemies), so increasing the size of the aliens to Its correct size (towering beasts) would cause hitbox glithching; i mean, you would hit them even by shooting to the (air, or space) hitboxes next to them.
Making the aliens as they should be would requiere a complete new engine, prepared to manage incredibly huge enmies that would make you turn your mouse view up anytime you met a standard alien head on, not to mention a praetorian. That's why I can't stand what has happened in avp2010 and ACM again; they had the perfect chance to create and portray the true scary monster the alien was once (once and for all)l, but Foxtards again ended up pleasing the cancer the casual audience is, and forced GB and Rebellion 8that's why I prefer to believe, but not sure yet) to make failaliens again that could please and appeal both the casual cancer and the kids, or which is the same..=$$$$$
If you allow me, I would like to give you an approximate correct reference for you to use next time (with another engine in another mod If it allows it) on the classic human born aliens, no matter a Classic Cameralien or iconic's Giger monstrosity (they actually size the same, both were +8 foot tall, so does the vicious runner when on Its two as well). You may find that perfect reference I'm talking about in avp2010 praetorian. Yes, that should be the correct size of the standard aliens (you have to look up to see Its face when It stands onn Its two right in front of you). They will tell you that's too much, but you know that's the truth right?
Well, like I said good luck on the project mate, and see you again on your next one.