It doesn’t really work like that. When a character takes an action:
a) it checks to see if the character’s skill level for that action is too high above the enemy to advance
You can advance to up to the enemy’s level + 5. For example, if you use a long-blade attack on a bandit who is level 20, you get a chance (see b) to increase your Long Blades, Blades, and Melee skills as long as each of them is below level 25. The minimum cutoff is 20, so you can get all the way to 20 fighting just the gladiators in training (they are level 10).
b) The chance to increase is based on your skill level; at low levels, it’s almost guaranteed that you will increase your skill on every action. The higher they get, the smaller the chance becomes. It’s a bell curve (like when you throw a pair of dice, you have a better chance of getting a combination totaling 7 and least chance of getting 2 or 12) – so basically everything is weighted to pull weak skills up to the middle (50 or so) very quickly, and then advancement after that becomes progressively more difficult.
The way you thought it worked is actually quite interesting. I could have done it that way, but I didn’t want it to be so hard defined – in other words, I didn’t want a system where if a character swings their sword exactly 100 times, they are exactly skill level 40 (or whatever). Then you’d be sitting there in battle counting sword strokes instead of having fun trying to win the fight.
I’d like to come up with a way to let you know that you cannot increase a certain skill when acting against a certain enemy (based on skill level comparison) so that you really know when it’s time to move on and find some tougher enemies. I think I will try to incorporate it into the target box somehow. More on that later…