Why is CR tied so strongly to size? Fine creatures, let's say, might not realistically have 100 HP, but since when did realism step into the picture? I mean, a 2 or 3 HD Tiny Fey becomes even scary for even level 4 parties when you throw down DR and Energy Resistance, high-speed and high-maneuverability flight, stealth bonuses, tumble bonuses, and poisoncraft (not natural poison, but venom-bladed weapons). I'm thinking there's a reasoning behind this, so I'd like to hear it before I either bash the system or try to playtest it. Also the inverse - who said a Large creature can't be CR 1?
Incidentally, other than the size thing here I think the system overall is a strong addition. While I see a few other points that may/may not be kinks, overall it's really strong and just needs a few tune-ups before it's just right.